OSX uses VM from the system drive, which is why it's a good idea to keep as much spare space as possible. You may also notice LW is a little ram hungry too. So having plenty of ram helps also. On my old computer I had two drives, both partitioned so I sent my downloads to a different partition to system drive. (I had 1.5 GB of ram on old system.)

Unfortunately there's no real method of increasing VM use other than more space or reducing its need a little by having more ram. The methods which I suggested for decreasing LW's use of VM is all I know of. Other than that, later versions of Java will be slightly more efficient. However Mac tend to stop developing Java on each older version of OSX. My new system uses OSX 10.5 and Java 1.5, however it also has Java 1.6SE installed. OSX 10.4 only has Java 1.5, OSX 10.3 Java 1.4, etc.

BTW OSX uses VM for all OSX applications. But it doesn't appear to have a function where VM can be increased or decreased, unlike some graphic programs do in their own preferences. Faster drives will read back VM faster I should suspect.