Do you mean 20MB over and above what is used by the save itself? Try running Scandisk (it is called Error Checking, or something like that, in Windows XP). With a FAT32 file system (Windows 98/ME, possibly XP) the free drive space listed can be incorrect (this is a more common error than lost clusters or cross-linked files).
1GB of saved game folders will zip to under 200MB.
