I would suggest that maybe adding another gig of RAM might help out considerably with your performance issues. Especially with TC.
SH4 really needs at least 2gig to perform at it's best..and even then, as Leo states, you will need to tweek your graphics card adjustments to get a good balance.
Look at this thread for more info...
http://www.subsim.com/radioroom/showthread.php?t=122928