No standard, compiled Windows applications will work. Ignoring all the details, you have two major barriers to running Windows applications on the N900:

1. Windows applications are written for, well, Windows, and Maemo is Linux.
2. Windows applications are compiled for x86 and the N900 is ARM.

Wine converts system calls for one OS (Windows) to that of another (Linux). So, that helps with #1 above.

So, now we're left with #2, the problem that even if Wine translates system calls from Windows to Linux, they're still gibberish to the N900's ARM processor. We've a fabulous translation dictionary, the best there is, but the person we're giving it to only reads Braille.

So, compiled Windows applications like Word and most games are out. On the other hand, if you have an open source Windows application, you're now closer to getting it running on the N900 without having to port it to Linux.