http://www.cannondale.com/bikes/index.htmlAnyway, my opinion on the difference between 26 inch wheels (What most Mountain bikes have) and 700 cc Wheels (Which Most road bikes have).
The 700cc is slightly larger than the 26 inch wheel (The 700cc is sometime called a 27 or 28 inch wheel, through nether term is technically correct, the 700cc is a French designation of the most common wheel on Road and road Racing bicycles). The larger diameter of the 700 cc makes it easier to peddle up hill (if you have the gears) and on flats. The reason is the gear to wheel combination is "wider" do to the larger wheel size (i.e. in any particular Gear, the wheel of the 700cc will be going FASTER than the same wheel if it was 26 inch do to the 700cc larger diameter). Remember one thing the narrow the tire the more pressure you can put into the tire without it breaking do to excessive tire pressure. The Higher the tire pressure the less roll Resistance the tire endures and thus the easier the bike as a whole is to peddle.
Wheel the 700cc is a more efficient wheel when it comes to peddling efficiency, the 26 inch can be made to a wider, as opposed to the taller 700cc, diameter. The reason for this is the 26 inch was first used in rural America on dirt roads (roughly 1900-1960). This type of bike was still around when the Mountain bike craze started in the late 1970s and became big in the 1980s. The wider tire provided more traction on dirt so was preferred to the narrower tires of the 700cc road bikes.
This is the difference between these two sizes today, the 700cc tend to be narrow (permitting higher tire pressures and thus less road resistance thus faster speeds) while the 26 inch provides more area coming into contact with the road surface providing more braking power and more tire on the road if that is a problem (It is a problem on Dirt roads and going Cross-Country, it is NOT a problem on paved roads).
Now there is some overlap between the two tire sizes. For example I have 1 inch wide 26 inch tires on my Trailer to my bicycle (i.e. roughly 25mm wide). My sister has 35mm wide tires on her Hybrid Cannondale which has 700cc tires. Thus the tire on my Trailer while 26 inch tires are NARROWER than my sister 700cc tires. That is NOT the Norm, most 26 inch tires, today, tend to start at 1 1/2 inches (about 37mm) and goes up to 2 1/2 inches (about 62mm). While 700cc Tires go from 17mm (3/4 of an inch) to 35mm (1 1/2 inches). Please note all sizes are approximates given the that tires expand, contract and even wear down.
While there is an overlap the General rule still remains the same, the 26 inch is wider than most 700cc tires.
How wide a tire can you put on your bike? The answer is as wide as the difference between the stays of the bike. My Cannondale can take tires as wide as 1.9 inch (through I am presently using 1.5 inch tires). My Phat City bike can take 2.25 inch wide tires. Most hybrids can only take tires less than 35mm (i.e. less than 1.5 inches).
Which is better? For off-road use the 26 inch do to its generally wider tires. For pavement, the 700cc for its larger size and thus better efficiency.
Last Comment on Tires, watch the tires on rims on most bicycles. While the higher end bikes tend to have tires that fit the rims, many do not. The reason for this is narrower rims are cheaper than wider rims, but people want wide tire bikes. Thus in many bikes you will see wide tires on very narrow rims (This seems NOT to be a problem with 700cc tires do to the fact 700cc tires tend to be narrow compared to 26 inch tires). For example my Bike Trailer came with 1.9 inch tires on very narrow rims (I would blame the manufacturer but I ordered the Rim and tire combination before I knew any better). I ended up replacing them with 1 inch tires for the rims were so narrow the proper size tires were only 1 inch wide tires.
Here is Sheldon Brown's Article on tire sizes, but please note while he mentions other sizes than 26 inch and 700cc, the bikes you will be looking at will tend to have one of these two sizes:
http://www.sheldonbrown.com/26/index.html1/2 way through the article you will see a Chart on what tires fit what rims. I have seen this chart violated on a regular basis, try NOT to do so.
More from Sheldon Brown on Wheels sizing:
http://www.sheldonbrown.com/tire-sizing.htmlNow, I know you are female and I want to make one comment on 700cc and 26 inch bicycles. Most women are smaller than most men, if you are small even for a women you may have a problem finding a bike that fits you. In such a case you may want to look at the 26 inch bikes do to the fact the 26 inch bike is marginally smaller than the 700cc bikes. If you do so have the bike dealer switch out the old knobby wider mountain bike tires for a narrower slick (If you plan to ride only on pavement or on a bike trail). I mention this for I have a couple of sisters who ended up on 26 inch bikes NOT because they wanted a 26 inch bike, but the 26 inch was just that much a better fit than the 700cc hybrids. If you are to small for a 26 inch bike (if you are you are VERY small even for a woman) there are some 24 inch bikes in the market place (and some women specific bikes like the Terry).
For more on the Terry see:
http://www.terrybicycles.com/Terry makes women bicycles, these are design for WOMEN not men's bikes in pink or with a down draft tube so your dress does not flip up while you mount your bike.