* It would help to know what games you intend on playing and the size of monitor...you don't want to get too much more than you need.
* When putting a $400 graphics card in that Emachine, the bottleneck is going to be the CPU...the Athlon64 3200+ isn't a processor I'd build a gaming PC around.
* You'll almost definitely need to replace your PSU in order to handle the new card...Emachines and others don't give you much cushion in that department.
In short, the RAM upgrade certainly does help but that does not have the makings of a true gaming rig. As such, I'd go for a graphics card that's cheaper and more geared for the system it's going into. (Your star QB can only do so much when the wide receivers are second-stringers.)
In any case, have a look at the selection from newegg.com and see what previous buyers have to say. If you're still set on a high-end card then have a look at the 512MB GDDR3 Radeon X1900 XT and GeForce 7800 GTX. Otherwise I'd stick closer to $200 with the 256MB GDDR3 GeForce 7800 GTX or Radeon X1800 XT, which do remarkably well for half the price.
Hope this helps,
I'm a gamer and i need a new GPU. I'm using an Emachines T6212 with 1.5 gigs of ram but no other changes. I'd like to keep the price below about $400. Any suggestions?