Hallo:

Yes, you can, but only if you act careless. To explain a little bit:

A virus or a worm needs to executed to propagate; executed like a program.
So:

Very unsafe:
- any .exe or .com files, for they are programs which could be infected.
- .vbs script files; these are programs also.
- .bat files (rare)
These files could also be zipped, unzipping is safe, but have ALWAYS a look what will come out of an archive!

Unsafe:
Any html-code with embedded javascript (mentioned only for completeness)
.doc .xls files for M$-Office; they could carry a macro virus.

Safe are:
- Any files which are not executed but interpreted by some other program like:
.mp3 .mpeg .avi .gif .jpg etc etc etc....

Remember that is never bad to have some kind of virus scanner and to USE it sometimes! And, remember also, that a firewall will not protect you against infected files.

But do not be disappointed, with a very little bit of caution you are on the happy side; the dangers are little and the enjoyment is great!

Happy gnutelling :-)
Greetings....