usually the cards are too slow to really do anything for you. Run HD Tune ( http://www.hdtune.com/ ) on both your card and your HDD and compare the access times and the data transfer rates. If the card is better in both disciplines, then it may be worthwhile. But don't expect wonders.
The best is to add RAM (which is dead cheap these days). Run a scan from this website ( http://www.crucial.com/index.aspx?g...85393:pyvl99bklaoaac96jqyaaaap:20081213201317 ). Then you know what your options are and what they cost.