Memory Problem

[z7917]

Hi.
I just installed ispCP omega.
Its like working smooth on my VPS but seems like it eats up so much RAM that the VPS crashes.
I have like 512mb and after Apache2 was started I have like 5 minutes to do this and that and after that its all working further but I'm kicked out of SSH as well as cannot login again.
When I try to start a new process i get: Cannot allocate Memory.
What actually makes no fun. Lol.

Is there any hint you can give me how to make sure that wont happen again? Cause I always need to ask my Host to reboot the VPS. thats not so cool.
Thanks for your Help.