[edit]  this is an old answer and win 7 is now available since I posted this. See below

Hello,

  As Windows 7 is still in beta you are right there is no official support for this platform.

So any advice given below is for an unsupported platform that may or may not work

As far as I know Windows 7 is a 64 bit platform (edit: it's available as 32 bit too) and I would suggest if any version would work it would be the "Windows 2008 x64" installation media.

This can be found on OTN

http://www.oracle.com/technology/software/products/database/index.html

If this does not work then you will need to wait for full version release of Windows 7

and Oracle to certify this.

Hope this helps.

John

 Oracle has released 11.2 Oracle Software, which is the first version supported on Windows 7. It is available at: http://www.oracle.com/technology/software/products/database/index.html

 Thank You,
    Jill