The Ti4800 is by absolutely no means a bad card, it's just that the 5900 is a MUCH better card. I doubt you'll have any problems running any games for a little bit, and if any insufficiencies come up, there's nothing Powerstrip can't fix eh?
ill go for the 5900 thx. reasons being its much faster even tho in games for now both cards would give roughly the same output cept when aa and all that is switched on. and 5900 is dx9 so emm yea...oh but drawback, with the 5900 */me hears vacuum cleaner but dont know where its coming from =\