question to hook_search[_preprocess] or ways for hook into searchprocess

hi,

i try to build a little widget where i need to write an entry to database when somebody searches for something(standard-search).
problem is:
using hook_search_preprocess is not only fired on search ,also when indexing content. and there is no parameter to differentiate the cases.
using hook_search delivers the searchtext only to the module which is the aim of the search(standard is node) so my module dont get the searchtext.

perhaps could somebody give me a hint how to do this with this hooks or with another aproach.

thanks
peter