make sure you have the locate packages install (and you really really must have already) with rpmdrake, and try using it as root. if it doesn't find it then try /usr/bin/locate as a full path name. if that finds it then it's most likely to be a screwed up path (check with "echo $PATH"). if that's screwed up then maybe you fiddled with the path in .bashrc or smoething?
oh and gkrellm *shuold* be /usr/bin/x11/gkrellm. also try using "which" and "whereis" to locate programs. all similar but do slightly different things
oh and don't use LimeWire.