Usually there's a reason that they're priced that way (market uncertainty, debt, etc), but Palm and 3Com is a good example when it works out. You may have problems shorting though.

Sell shares/buy puts on the overpriced company (in your example, Palm), buy shares/buy calls on the underpriced company (3Com). Usually implied vol is pretty high, so you'll definitely pay a premium for the long options position. Alternatively, you could sell premium, but that is quite a dangerous position for a retail trader.