looks like the boot manager files are on the 50gig C: drive so formatting the vista drive shouldnt affect boot 
If your worried as insurance you could create a system recovery disk from the "backup and restore" link in control panel which will restore the boot manager files if they get lost
Trust me I'm a teenagers father!

Operating System Windows7, vista, xp, snow leopard
Computer Type self built desktops, laptops, NAS
CPU Type and Speed AMD Phenom II 940 Black Edition
Motherboard Chipset biostar TF8200 A2+
System Memory Type 4x 1GB Corsair TWIN2X2048-6400 (XMS2)
Video Card Type and Speed HD5770
Computer Monitor ASUS VK222H 22"
Hard Drive OCZ Vertex 2, WD3200AAKS sata 2, WD5000KS, 1TB Samsung Spinpoint F3 SATA2
Optical Drives LG GSA H10a DVDRAM
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Anti-virus Software MSE
Computer Skill Level Certified Professional
Windows Experience Index 7.3