I have 4.8.0 PRO paid version. It crawls on a Pentium 4 with 512 MB ram. Why? Could the fact that I upgraded to Java 1.5.2 have something to do?

When I start LW, it basically overtakes the entire RAM, all other software that is open suddenly stalls, until 5-7 minutes, after which LW appears and all is back to normal. How can I reduce this startup time?