After installing Windows 7, my MacMini won't boot Lion anymore
So a guy in MacRumors ask me why I didn't install the Boot Camp drivers in Windows yet - I don't know, nobody mention this before (or I really miss this part). The package is more than just drivers, will install a control panel similar to OS X and will change the boot either - just what I was looking for. After install it, I could finally boot from Lion just by selecting in the list of the control panel.

Unfortunately, I cannot copy-paste the link for the Apple page about those drivers because the site will auto switch to pt-br... I think you will find it easily by searching support.apple.com with google. You got to look for instructions about installing old versions of Windows in old Macs, there is an article about this. Just a warning: each system/Windows require a specific package and version (4 ou 5). Pick the right one and you will be happy.

If you got the link in english, please share with us.