You have really got two options;
1) Keep the side bar and have a slowish running system with explorer useing random amounts of memory.
2) Run though a simple tweek guide and have a fairly stable system but without the sidebar.
Personaly I feel that later alpha releases will have the sidebar mastererd so these releases should be used to test the OS as a whole and not just one component.
I have been running Longhorn 4051 now sine the PDC and after ironing out a few bugs and tweeking it a little I have a good stable system.
If you want to test the operating system use this
Tweek GuideIf you want the sidebar use the file below to do so.
Vaughaag