You did not say how big the drive is--or how full all the Windows partitions are. For example, if each partition is only 60-70% full, you may be wasting a LOT of space.
If you want to access all your data from Linux, then having all the data in FAT32 partition(s) is a common approach. You can also use ext2 or 3 and get a Windows tool to access that.
As already mentioned, just installing another drive may be the easiest way to go. Anything under 100GB is REALLY cheap.
Since you already have all that important data backed up, we won't mention that anymore....