The are dual boot guides in the Windows 7 forum here.
If they make sense to you, I'm pretty sure you could:
1) Backup your OS X disc
2) Use a GParted LiveUSB to shrink the MacOS partition and make a new fat32 (or NTFS) partition for Windows 7
3) Install Windows 7, after first formatting the partition made with Gparted again with the Windows 7 installer.
4) Restore you MacOS data
5) Use EasyBCD (google for version 2.0 beta) under Windows 7 to have Windows bootloader boot between Windows 7 and MacOS
6) Boot with the DellEFI disc (can't remember its proper name) and re-run DellEFI to make the OS X partition bootable again.
Mini1: Vostro A90, Black, 2G, 1.3 Webcam, Bluetooth, 64G SuperTalent, OS X 10.6.4
Mini2: Mini9, Black, 2G, 0.3 Webcam, Bluetooth, 32G RunCore, OS X/Win 7, internal PCI-e SHDC Reader
Mini3: Mini10v. Black, 2G, Webcam, 640G HD, OS X 10.5.8/Win 7/Ubuntu [Hibernate w/NBI 0.8.3 RC4] Dropbox Referral