AppleSearch 1.0 forces the "AppleSearch Indexes" folder to be at the root of HFS partition. This is fine for HFS disks, but for the UFS disks there are times when you want to move them (if, for instance, /users is a separate disk and you want the indexes there).
Here is a workaround you can use:
1) Start AppleSearch and create the information source indexes in "/".
2) Quit AppleSearch.
3) Move the index to wherever you want them to exist.
4) Restart AppleSearch. It will ask you where the indexes are, navigate to them, and then AppleSearch remembers the new location.
5) Index as usual.
Also, you may want to have fair amount of available space on the "/" directory. AppleSearch uses this directory to store temporary files when reindexing, which can be large at times.