hmm, in case you still wanted to know...
during sexual intercourse, the friction can cause tears in the vaginal lining no matter how many times you've already done it. a way to alleviate this problem is to buy a bottle of water-based lube (i personally endorse astroglide, but there are plenty of brands -- check out the Safer Sex Condoms and Lubes forum for details).
Apply a drop of lube to the inside of the condom (not too much, or it may cause the condom to slip off the penis), and apply as much as you want to the outside of the condom and to your vulva. This'll reduce friction between the penis and your vaginal lining.
"Go that way really fast, and if anything gets in your way ... turn." Better off Dead starring a teenaged John Cusack.