If you really facing a problem with bootloader, you are to follow the instructions in the tutorials Startup Repair
; and . Startup Repair - Run 3 Separate Times
(for the both, you need either the windows 7 installation disk or the recovery disk; about which seavixen32 and theog have told earlier. If you dont have any of these, let us know.)
The best way to install Ubuntu in a dual boot steup is the instruction that seavixen32
is posted ... the Option One
of the tutorial Dual Boot Windows 7 and Ubuntu
There is no such trial version of Windows 7 . If you can install it, it will be a full version if you provide your license key during installation , otherwise it will be stopped after a few days .