If you're using XNS (which you are, from what I can tell), your mount.cfg should look like this:
// Uncomment desired games
// cstrike is enabled by default
"mountcfg"
{
"cstrike" "C:\GameContent\cstrike"
"tf" "C:\GameContent\tf"
"dod" "C:\GameContent\dod"
}
The TF and DOD parts are optional- remove them if you don't need the content.
XNS's servers is hosted on a Windows OS, which means the paths will contain \'s and a drive letter (C:).
Also, CS:S content is installed on XNS's servers outside of visible range. It's there, in C:\GameContent\cstrike, but you can't see it.
Note: This is coming from a server started before the new Source performance and cheaper slot pricings XNS released. Try these first, but be warned that things may vary.