I am using FC2. Please ignore if it is irrelevant to slackware.
I tried compiling gtkpod and failed to satisfy all the required dependencies. I ended up installing gtkpod-0.94.0-1.1.fc2.rf from an rpm.
I had to install the following rpms:-
1. faad2-2.0-0.lvn.0.2.rc1.2.i586.rpm
2. gtkpod-0.94.0-1.1.fc2.rf.i386.rpm
http://www.linux.is/howto/howtoview.php?id=294 will may help you install and use rpm on a slackware system.