I have got a Virus TI2 61 key, with an AMD 64 X2 3800+ overclocked and running at 2.25 GHz with 3gigs of RAM and Windows XP pro, been using the Virus as my sound interface until I get the one I really want, and well I have not had a lick of trouble with latency using it with FL Studio 8, Live 7, and Sonar 7, but the first thing I do is setup the latency compensation for each respective DAW. Something to think about, have you got swap file enabled, or virtual memory running, if so turn em both off. Make sure you disable any Virus protection while you are in the midst of working, and make sure you are not signed into the internet at all,ie chats, ect. Then pull up you task manager and see how your memory is looking, you might have some background progs that are eating away at your physical memory without even realizing it.
Good luck, if I can get it up and running I know anyone else can
Cheers
Nobl1v1on