Also, the word count is for a manuscript in Standard Manuscript Format (SMF), meaning Courier 12 pt., six inches of text, 25 lines per page, no more than 68 pages.
Kary's correct. As a rule of thumb, following SMF gives you roughly 250 words per page at the *lower* limit. To be on the safe side, I'd personally try for around 60 pages myself. Don't forget that SMF is typically double-spaced (see http://www.shunn.net/format/story.html
, though venues do vary greatly in their requirements).
For the novellas you've seen in the Hugo list, keep in mind that they're almost always from very-well established writers (including our very own Brad). It's very rare to see one of the big magazines take a risk on a complete unknown for a novella length work. It does happen, but it's difficult to break in writing longer work (as both Dr. Bob and I know...). The contest's word limit is actually quite generous in the context of a contest for people looking to break into the pro markets and I don't know what I would have done for my first sale if the contest didn't exist.
The new TOR imprint is probably the best market in terms of prestige and pay for the novella length at the moment. Gigantasaurus and the Panverse anthologies are also prestigious. All are very hard to get into. There are probably a few others around that I don't know about, but they're the ones that come to mind.