Not only vmware, there also exists Virtual-PC. I run it on ny PIII-550 (256MB RAM) and looks OK. I've allocated 64MB for the Linux system.
Also there are some bugs, like when switching from WIN to the virtual OS, back and forth, however their so called add-in tools are meant to deal with such discrepancies. You could try Virtual-PC with the add-in tools installed.
Personally i'm very satisfied with the speed (i won't run Q3:Arena but for all other apps it is satisfactory). One other thing, is that the X-Window system is very heavy so some latency is also due to that.
the_penetrator©