Since you still have all your data on the span with disk 2 and 3, you can:
- Create a new BASIC disk (disk4)
- Copy all data from the span to the basic disk 4.
- Shutdown the VM
- Remove disks 2 and 3.
- Remove disk 4 (remove from VM, remove, not delete!)
- Add the disk file back as disk 2
How to do this precisely depends on your software. VMware? Qemu, virtual PC, ... ...
And as always, make a backup before you do this. Better safe than sorry.
An alternative is to copy the VM.
- Create a new VM with two basic disks.
- Copy the disk file for from the working install (OS disk only!)
- Use the network to copy files from the other VM to this one.
Effectively you do the same, but you keep the old VM around rather than making a backup.
If you do this you might want to double check how your VM software allocates MAC addresses and you might get a duplicate name on network problem. (The latter is a guess. I know Xp and win7 will throw that, but I never needed to do this with server 2008).