Do I look like I smoke rocks in the picture I recently posted in the picture thread? xD

http://achaea.com

Most popular MUD available right now, not pay-to-play but you can pay-for-currency sort of deal, which you can buy your skills with. I've played it the last 4 years or so, and the combat system is immensely complex and entertaining, if a bit unbalanced in some rare cases. Overall, a very indulging experience that I've enjoyed for a while and only recently played less.

256 MB RAM.
1.7 GHz Celeron.
3 year old Dell.

(I won't go into actual detail.)

Escape From Lego Island!