Ooops sorry I only read half the question.
When working with SolidWorks, yes Virtual Memory is a critical thing... I reccomend 4x the size of your Physical Ram. Another thing that helps is if you can set up a logical partition devoted to nothing but swap...this helps your saved data from become fragamented so quickly.
Another thing to keep your s ystem sharp is to make sure and run "Unfrag" first which eliminates the Compound files that SW has created.... then Run Defrag. That helps keep disk performance up.
Your lines disappearing are definately a Vid card issue though, if you have the means, I would replace it with one the approved cards, I run a 32Mb FireGL1 with good results, and my other workstation has an Nvidia RIVA TNT2 32 Mb (my home workstation) and it has a few graphical annoyances. So it happens
Ciao
Jon