Windows and Linux

If i install Slax, can I still use my microsoft windows xp?

yes with dual boot if you don't want mess it up with windows!

Its not recommended to install Slax on HD. I would suggest you to go for any other user-friendly distro like Ubuntu, Fedora or SuSe. Check distrowatch.com.
Check the link in my signature too.

Dual boot is default in all Linux distros. Just create a free space for Linux and install it.