well you did not give enough information

is the graphics card an ati 9800? or an nvidia 9800? is it pcixe or agp?

you can build a decent computer for 900 or less, that is unless you need to upgrade everything.

what type of computer would you like? premade or are you capable to build a computer?

is this just a gaming computer or would you be doing video editing or what not?

do you want the latest technology or would you prefer to have what works and cheaper?