well thats a pretty hefty budget and really depends on what your going to be using the computer for.. im assuming since your pretty interested in the 9800 you are a gamer
so here's a basic build off the top of my head...
2gb or 4gb of ddr2-800 crucials
whatever hdd space you need
dvd burners, etc
Tuniq tower 120 or Thermalright ultra 120
620W Corsair PSU
evga 8800gt 512/8800gts 512 (however im not exactly sure when the new 9800's are really gonna come out they say feb...)