Using the HHonors Reward Exchange you can transfer miles first to Hilton and then consolidate them in the program of your choice (probably the one that already has the most miles). The major disadvantage to this is that (a) you lose around 60% of the transferred miles in the process, depending on the airlines involved and (b) it's verrrry slow, so plan ahead if you know that you'll need a specific award in the future.

You mentioned that you have some miles with USAirways. If you have any with American Airlines, you can combine the two to get a joint award, so that might be an option also. (What I would do in that situation is transfer the miles from TWA, Continental, etc. to American since they have a more favorable exchange rate with HHonors, and then combine them with the miles you have with USAirways).

We can give you more specific advice if you let us know more details.