So I can only guess badly. Try the Computer Help forum as that issue is not a Dell one but an OS or account issue.
But here's the advice for XP, Vista and 7. Let Windows manage that. There is NO SPEED TO BE GAINED here.
My i1545 will not let me change the virtual memory size. It refuses to set and remains "system managed". Any ideas? Thanks.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic