SBS 2000 crashes

Hi,

endironment:
1 SBS 2000
1 Server 2000 with AD, same domain
15 Clients

The main Server (SBS) crushes: it often stop respondig, you can moove the mouse, let the client use some services but you cannot run anithing new. It appears it run out of memory. It appears also it doesn’t use correctly the page file. The Server as 512MB ram, but not too much space on the disks.

Please HELP!!!

thanks
Fabio