Notice that the -lib flag always requires Unix styles slashes. This is the case even on Windows.

You may also want to use the -nosound flag. For instance, my PC has problems using audio (it leaks memory), so I just turn off the audio part of Pd. However, other people can't get GEM to work if the -nosound is used (on Win95). You can also try the -nodac or -noadc flags (for digital-analog-conversion only and analog-digital-conversion only).