MSN actually uses Yahoo! Search Technology, which is a hybrid best of breed solution made up of Inktomi, AltaVista and Fast.
MSN does not take the full set of YST results but rather is a smaller subset. MSN announced in July that they would no longer be taking PFI pages from any source i.e. Inktomi Search Submit, Overture Site Match or Overture Site Match Xchange.
The only way to get into MSN now is to use the Yahoo! Free Submit (many links to this already posted) and wait. Building incoming links will speed up this process and of course, should be part of your online promotion strategy anyways.
Of course, when MSN releases their own spidering technology, you will need to make sure you are included in that index.