Might be a bit of overkill, but this is what I did...
I have 2 computers that I have wallets on. The first one was installed with all the default settings and runs all the time. This is the one I use to receive all transactions (but using several receiving addresses). I intend for this to be a day-to-day wallet that never holds more than several Bitcoins at any one time.
On my other computer I have my main 'bank wallet'. I installed TrueCrypt and made a 5GB volume (AES encryption, SHA256 hash, 11 character alpha-numeric password). This encrypted volume has both the Bitcoin program installed on it as well as the wallet data. After the initial install and getting the full blockchain downloaded, there is no need to have this open unless I am sending or receiving coins from it. At most it shouldn't need to be open at any time longer than about 15 min; the time it takes to update the blockchain to what is current plus the block that holds your 'change' transaction, if any.