/proc/ide is a sub-directory of proc, not a file, so you can't use cat. You'll have to navigate down into /proc/ide's subdirectories, where the actual info files live. Of course, if you have X installed, this can all be done with the many GUI-based system monitoring/info tools available in KDE, Gnome, etc.
BTW- Strangely enough, trying to cat any "real" directory/filesystem will give you the slightly more informative "cat: /<directory_name>: Is a directory" error. I think because /proc is a virtual filesystem, you get the "Invalid Argument" error instead. Any gurus out there have the definitive answer on that one?