In the past, when ive done a dual boot, when booting from either partition, it would come up as C:, so that when im running in either, the main path would be c:\.... but ive just installed Windows7, as a dual boot, with vista, and when booting from w7, the current partition is D:, so that all my apps are D:\... How do i get around this? How do i duall boot so that both partitions come up as C:, when you're actually running fromt he OS on them

You don't.

In your offending OS, go

Start -> Control Panel -> Administrative Tools -> Computer Management -> Storage -> Disk Management -> Remap your D: drive to C: or whatever you need to do.

Windows does not allow changing the drive letter of a boot volume.

The reason for this is that many things in the system (including all installed programs and some components of Windows itself) depend on absolute file/directory paths which are stored on registry and various configuration files.

Now, imagine that all of these paths would be invalidated - the programs would effectively be missing, and Windows itself couldn't start. It is not a viable solution to search and update the references either, because while Windows could repair itself, the system core doesn't have any innate knowledge about third-party software paths - or more accurately, where references to said paths are stored.

The drive letter assignment can be somewhat random even on a single-OS clean install, depending on the drive configuration and the order in which the BIOS happens to enumerate storage devices.

All this said, it is best to leave the thing be and code your own software so as to not use hard-coded paths to C drive.

Windows itself does not rely on any particular drive letter, but the system location is fixed during the OS install and it is required - for the reasons mentioned above - that the OS instance will actually stay there.

Unfortunately, some programs do assume that they can write to C at will; this is bad practice for many other reasons too.

I forgot to mention that if your C: drive letter designation is free (though I assume not, in this case), you can use the subst command to map it to a specific physical path. However, this remapping does not persist after you log out.

Sorry, i didnt mean a fix to the problem. I meant, how would i reinstall and get the result i want. Or is that not possible either?

I dont know how i did it in the past, but i had 2 vista partions, and although they were C: and D: when viewed externally. When booted, they were both C:

If the partition of the second OS instance is initially completely free (as in, not even formatted), the install may assign C: to it. However, this is not guaranteed in any case.

In general, most people that dual-boot will actually prefer that both OS instances see each others' boot volumes. This enables easy file transfers between them.