Probably your best bet at bestbuy for gaming under 1.5k
as sad as it sounds, that 1.5k computer is about equivelent with my 800$ computer I built myself. If it comes down to it, bribe your mom lol. Tell her you'll give her 200$ if you can build one yourself. You'd be better off with a custom built from monarchcomputer.com or something and paying your mom 200$ than buying a shatty prebuilt.
edit: OR if you have to buy a prebuilt, buy a really easily upgradable one with a good cpu and motherboard, and upgrade ram to 1gb and get a 6800gs video card.
Just be sure it's pci-express motherboard, and hope it's skt. 939/pc3200 ram
edit2: oo or get this prebuilt
for 650$, and buy a 6600gt or 6800gs video card (130$-210$) and you're set to go.