Is it possible to convert to Hinduism? Do the various traditions have different opinions on the subject?

I have a few Hare Krishna friends and I know that their movement is very accepting of converts. However, I also know that they don't represent mainstream Hinduism (at least what you encounter in America and as much as you can actually discuss a "mainstream hinduism"), and I'm wondering how other Hindu groups might go about accepting (or not accepting) converts. I haven't been able to find a good website that discusses the issue and have only seen the topic in a book once. Any information would be welcome.