I'm using MOSS 2007 and I want to wipe out the search index and do a full re-crawl of one of my content sources. I see the link to 'Reset all crawled content' but I don't want to have to re-crawl the other content sources. Is there any way to do this?
I don't think there is a way to do what you want.
The closest available way that I can think of would be to remove the content source, wait for a few crawls to happen, then re-add the content source.
The reason you need to wait for a few crawls to happen is that the search index doesn't get cleared of the data for the removed content source right away. During subsequent crawls the data is removed from the index. (You should be able to see errors in the crawl logs that the data was removed)
You can temporarily remove all the Start Addresses of the content source.
Then SharePoint Search starts an automatic crawl to remove the data from the index. You may notice that the Current Crawl Duration field of the content source starts counting, even if the content source is in Idle state. (you can also check the Crawl Log to see which items have been removed from the index)
When the Current Crawl Duration field is empty again, you can re-add the start addresses.
There is another way. You can use federated searches. It's possible, I just wouldn't recommend it. It is really for merging larger indexes together for a single query like when you have multiple farms or you want to take advantage of an existing index of material.
So, if it happens often enough or whatever reason, it might be worth looking into. Sometimes knowing what the alternative is helps control frustrations with the current solution.