Vista - Please help! Vista doesn't let me download, unzip and itunes...

Hi,
I am really frustrated right now. I just upgraded my OS from XP Media Center
to Home Premium. I am using my default Admin account and I can't even
download any files from the Internet. After finishing downloads, suddenly the
window closes without saying anything and the file is not there. Instead of
saving, chose the "Run" option and still same thing.

Anyway I copied some zip files into a directory. Unzipping it, everything is
empty! Doesn't seem like it likes to unzip.

Some songs I purchased from itunes with DRM requested me to enter my itunes
password to activate it in my computer. After successfully doing it, yet it
doesn't seem to allow me to play the song and it prompts me to enter my
itunes password again and again.

I was pretty impressed with the beauty of Vista but this is making me nuts!
Please advise... would really appreciate it! Thank you!