You were doing good right up to the point you made the new partition the active partition.
Windows should be on the first partition of the first hard drive. This first partition should be made active. This would be a primary partition. You can have 4 primary partitions on one physical drive, but only one of those partitions can be made active.
Go back and fix windows so it is booting correctly off of the first partition which should be set back to active.
Then install Mint 4 to the second partition but don't make it active. Install the boot loader into the mbr on the mint install.
If all goes well you should have a working dual boot. I have heard that Vista doesn't want to cooperate, on some computers, but there are work arounds if this is the case. But first try what I suggested.