OK, gotcha. Looks like you could upgrade that TiBook to 1GB RAM for about $60 (2 x 512MB chips) plus the cost of installation, using prices from Other World Computing for the RAM. If you're at all inclined to do so, you could install the RAM yourself with instructions from Apple's web site. It's relatively easy.
Doing so would greatly speed up your computer and Photoshop, since the TiBook would have to use virtual memory much less often.
Incidentally, what speed is your TiBook, or what is the model number on it?
