Indexing and regular expressions

Is there any indexing technique available I can use when joining tables
with a regular expression pattern in pgsql?

I know one method for indexing strings that will be matched with regular
expression patterns, and that is using so called k-gram indexes.
Indexing the string "kjartan" with k-gram index where k = 3 would
create "kja", "jar", "art", "rta", "tan" as an index. Ofcourse it is hard to
decide the size of k and I'm sure in many cases mulitple k values might
be needed, depending on the situation.

I have not done any major survey of available techniques, but I was
hoping I could get some pointers here.

I assume pgsql always uses nested loop join when joining relations which are
joined with regular expression pattern?
-- 
Kjartan Ásþórsson
http://www.kjarri.net 
Tel: +46 (0)730 556705