Hey,

I just finished setting up my new dev environment on my work laptop.
There's some key elements to do this in a successful matter.

Start setting your win7 up normally.
When selecting harddisk, make sure you create a partition that fits your need and make sure to leave space for the VHD that will contain Win2k8r2.
After the win7 installation, reboot and put in your Win2k8 dvd.
After selecting language press shift+f10 to get into the winpe console.

1. Enter DISKPART to run the utility.
2. LIST DISK to see the available disks in your system.  I am assuming a single raw disk.
3. SEL DISK 0
4. CREATE PARTITION PRIMARY
5. FORMAT FS=NTFS QUICK
6. LIST VOL
7. ASSIGN
8. LIST VOL
9. CREATE VDISK FILE=d:\win2k8r2.vhd MAXIMUM=50000 TYPE=EXPANDABLE
10. SELECT VDISK FILE=d:\win2k8r2.vhd
11. ATTACH VDISK
12. CRE PART PRI
13. FORMAT FS=NTFS QUICK
14. ASSIGN LETTER=V:
15. LIST VOL
16. LIST VDISK
17. exit DISPART
18. exit WinPE command console
19. Install to the newly created 200GB (fuzzy math) virtual hard disk which looks just like a partition to Windows Setup

This is all there is to it, after installation, your system will boot up with a boot loader, and here you can choose between 2k8 and win7...

AWESOME!!!!!