With regards "dirty" records, heard recently that glue applied evenly over the entire playing surface, allowed to dry and then peeled off works a treat. Not tried this myself and I can't remember if a special sort of glue was required. Hopefully "jacksprat" will see this and explain more fully, 'cos he told me in the first place. As with other posters I would also suggest trying any cleaning method on an inexspensive record first.
Cheers Paul