Install more ram. lol
OSX has its own way of using ram & virtual memory. If you're seeing blank areas on LW's interface whilst LW is 1st opening, that's a Java issue not ram issue. Unfortunately Java 1.4.2 which is the highest version OS 10.3.9 offers isn't up to scratch. Java 1.5 has improvements. Mac's Java is not as good as the versions released by Sun Java for Windows & Linux.
As far as disk error goes ... it's probably due to lack of HDD space available. Check how much space is available.