for a hard drive controller setting that changes SATA to IDE or compatibility mode. This should allow you to install Win7 from a bootable DVD. With an older board, this may be the best and only option. I'm not sure what you've done to troubleshoot the DVD drive to figure why it won't boot from the Win7 media. I'd see if it would boot from other media. If not, you may need to replace it.
A friend of mine has anolder msi motherboard a KT8NEO. His harddrive is a 320 sata 1.5gb the problem is that we wanted to install win 7 but it wont boot the dvd on startup. So installed through win xp and when it finnished it locked up and upon restart files were messedup and it wont boot! So because hits MB is older it has to have special drivers load up for the SATA port! need a floppy! SO what we ended up doing is buying a 320 gb hd ide. Loading win xp on that and then installing win 7 on the sata drive. It installed fine but the system will not boot unless that ide drive is plugged in? Any sugestions? Everything is running from the win7 drive and when you look at it in diskmanagment its shows its a boot drive and that its healthy and all.