i'm round too and i ride!
Yes fat girls can ride and it's great. I started almost a year ago and i'm 240 lbs and 5'5". It's hard work up the hills, but I love riding my bike. I started slow and small. Riding into the city (12km) was a major major achievement. I was so stoked I could do it. This week I rode to work (25km round trip) three days in a row... a first for me. I'm pretty damned proud of myself. And i'll be riding again tomorrow... so that's 4 times this week :D .
I ride with 3 friends who do it for fun, they dont care how fast we go as long as we have fun. I know it's hard to find people like that, but they are out there! And if they are not around, hell I just go out by myself! I get excited when I overtake people (cos people usually whizz by me) and i've overtaken 3 in a year (and am looking for my fourth :p ). I felt so good one day when I whizzed past a woman (who wasnt overweight) and she said "does it ever get easier?"... so i slowed up and we rode home together while we chatted. It was her third ride and she was feeling down. I felt great knowing I'd made some progress, and we had the best chat and ride home together. So say hi to people when you pass, you just never know... they might want to ride with you!
So, fellow fat lady, please dont take any notice of those who make fun of you. People laugh at me when i rock up in my TE plus size biking clothes (god I love that someone makes plus size bike clothing - impossible to get here in Oz), but I could care less. I love my bike, I love riding my bike, and I figure every km I do on it is a bit more exercise I'm doing to take care of my body. And one day we might even be one of the thin girls!