OK. Try next:

1. Import key to 0.3.7 (as I understand, this stage works)
2. Copy wallet.dat to working direcctory of 0.5.2
3. run 0.5.2, and it must use wallet with balance from loaded key.

If something do not work - please be narrow, and exactly clarify, which stage fails.

PS: if [1] fails - Maybe, for upload your key, needed to use more old wallet version.