Sneak preview: How do I uninstall MAXDB instance?

Hello, I am having big problems installing the Sneak Preview.

I tried to install the complete package on my PC. However, the first installation of the portal failed. I assume because of memory problems. Now I have bought 2 gig of memory and installed the memory. Then I tried to continue installation, but this failed.

Then I tried to remove everything. Used SAPUNINST.EXE. That seemed to go okay, but now when I try to reinstall the J2EE + MAXDB, I get the message that an instance of the database still exists. I cannot remove, nor can I reinstall the MAXDB...

Is there any way to clean this mess up? Or do I have to consider formatting my PC?