I don't know of any free solution, but for what it's worth, most VNC clients on iOS suck.
Here is what does works (and it works even on iOS 5), I have been using it for years:
iTeleport | Home
It's hand down the best VNC / Remote Access implementation there is on iOS (they even have a patent on the touchscreen implementation)
SSH encrypted transmission
Can access Macs and Windows
Works from inside your WLAN, as well as from outside (e.g. connected on any WiFi, or 3/4G)
Seriously though, for me, this was the best $25 I ever spent for an iOS app. I wouldn't miss it.