I was curious to know how I go about making certain categories restricted to certain user ids. Kind of like having a VIP section. I've looked at a previous example that works for topics, but not sure how to go about it for categories.

If you mean a closed forums which is allowed for certain users only, take a look at the $clForums, $clForumsUsers options. Read: Manual - Private Forums.

Ah, Thanks so much! Sorry that this has probably been asked before and that it's even in the manual! :(

Though, I hope for others that search for this find this thread and see your link to the manual.

No problem, pal.

Is it possible to make a private forum visible to everybody, with only possibility to write limited to a certain group of users?

An archive forum is fine, but it requires granting users moderator's privileges to write in it. They will see others' IPs and so on, that I dislike.

You may get some ideas from this thread:
Private forum, but visible for everyone