Unlike some of the other demi-human RMAs, Gnomes are not also PC race in BX. For those of us that have knocked about the old Grand Duchy a while, we've run into the little buggers from Highforge as NPCs, but I don't know if I've seen them used as a "monster" in actual play.
First off, the stats. They aren't terribly interesting, but let's get on with it:
Gnome (from Moldvay)
MV: 60' (20')
ATT: 1 (wpn)
DMG: 1d6 or wpn
# APP: 1d8 (5d8)
AL: L or N
*Morale improves to 10 if a leader or chieftain is present
As mentioned, nothing exceptional in the stats. One mechanic to consider is that the little buggers have better infravision than dwarfs or elves (90' vs. 60'). It's possible that could become relevant.
The gnomes' descriptive text holds some fun tidbits. "Gnomes are excellent metalsmiths and miners." Lots of plot hooks there.
Here's the bit I love:
"They love gold and gems and have been known to make bad decisions just to obtain them."
Hoo boy! Is there some meat on those bones! Maybe the gnomes enter into a dangerous bargain for some shinies. Maybe they delve too greedily and too deep. Who knows?
Over at the BX G+ Community, Mike Hill pointed out that, oddly, the gnomes' Treasure Type (C) does not include any chance of gold pieces. I suppose it I were to try and explain that as other than the designers simply picking a table entry that yields an appropriate amount of loot without carefully referencing the flavor text, I'd say that the treasure section allows the DM to place treasure and to move values around. Maybe there are no gold coins, but perhaps there are ingots or lumps or ore?
Jumping from the monster listing in Moldvay over to Cook, there is a fairly extensive writeup of gnomes in the Karameikos wilderness section (X60). In fact, they are the only race described under the "NON-HUMANS" header. It's long enough I won't break the whole thing down here, but it's definitely worth a read. The layout of the defenses is particularly fun (It even has a map!). There is a typo (?) where the text describes summoning guard animals (giant moles) but later mentions them as giant ferrets. I assume it's supposed to be ferrets, as there is no monster entry for moles (giant or otherwise).