I'm having difficulty with my comp giving low frame rates I have 6 gigs of ram ddr2, 2.3 ghz amd quad core processor, biostar motherboard, 450 duel fan 1gb by Gigabyte. Is there any reason why I should be running Rift or any game at low frame rates??
Are you running at max details? Have you tried turning them down, or lowering your resolution to 1680x1050? If either of those improves your fps significantly, the answer is that you don't have enough graphics card for 1920x1080.
Anandtech, unfortunately, hasn't tested the GTS 450, so there isn't any useful comparison vs. other cards. I suspect that if you google "GTS 450 rift benchmarks" though, you would find some useful comparisons. Or maybe take out "rift" and just compare to other similar game benchmarks.
Another question is: what are the "low" framerates you're getting? 10? 20? 30?
As mentioned above, you could try lowering your resolution and/or details and see if that improves your fps, for a no-cost fps increase. Tom's had an article back in December about the effects of the various detail settings in WoW and what effect they have on your frame rate. Shadow quality, of course, is one of the big ones.
Assuming you don't have an nVidia northbridge motherboard (as they're not all that common), you can't SLI another GTS 450, so your next best choice would be to get a bigger graphics card, either a GTX 460 1 GB (as pacioli suggests) or an ATI 6850 for $175+.
I'd look at upgrading your processor as a worst-case option, as it's likely you've got an AM2+ mobo, which is old tech at this point, and you'd be better off upgrading to either an Intel SandyBridge setup or waiting for Bulldozer in the late spring, but either of those upgrades includes CPU/mobo/RAM, and isn't going to be $200.