I'm running into new problems with my new Slackware-installation every day...

It's quite hard being a total newbie on this, but also educational...
After discovering I have to compile wxWidgets and aMule to get this working on my old file-server (P200, 64MB) I downloaded what is said to download in the wiki, and run the commands in the wiki.
First problem is when I try to do the
mv src wxGTK-2.6.3 I get told that :
"mv: cannot overwrite directory"
Solved this by moving the files via my pc's explorer - as this is my fileserver...
Then I run the .configure, which ends with:
configure: error: C preprocessor "/lib/cpp" fails sanity check
I have gcc and g++ installed (for i486), as I just checked for them.
If they work as supposed I do NOT know... I've used Linux for three weeks and am not to experienced at finding out things like that. But they show up in pkgtool...
Anyone have any ideas?