i turned my dimension 3000 into the system listed in my specs below,,,that's about the best you can do with changing out only the motherboard, and then you can get an agp graphics card instead of pci card. the case is propriatory so you cant just buy any old atx form motherboard and have it fit....the dimension 4600 motherboard will fit and you can reuse everything and just get an agp card...i bought a 4600 motherboard on ebay for about 100 bucks. i had the intel pentium 4 @3GHz in my 3000, so i just stayed with that, but if you got the celeron, you may want to pick up an intel pent 4 to replace it...still not going to have anything great after that, but at least it wont cost you much and you can reuse everything in the 4600 board that you have now with the 3000 board..just get a agp card and the 4600 board....and maybe a pent 4 instead of the celeron processor and all should be about 200-250 bucks...or save that $ towards a completly new build with more up to date components...