Yep, they take standard cassettes.
Yeh, you may as well get a new rim while you're at it - To be honest there's no shortage of these hubs if you look around on the second hand market.
Rim wise, Mavic D521 (EX712? Someone clarify this if you'd be so kind :S ) are very strong and hold grinds well, but they're thin compared to the current crop of 38-48mm rims available now.
This means they won't fit in most UCI frames (Koxx's/ZOO's/Echo's etc) without some kind of bodge.
If you ride alot of street, have a look at an Onza Ronnie, if you're more natural-inclined, have a look at the new Echo 48mm rim.
Both are available from Tartybikes.com.
What frame and rim are you currently running?