I've done exactly this. First I get an rss feed for my full myspace postings (not just the first couple of posts) by piping it through Make Data Make Sense:
Make Data Make Sense builds the RSS feed on the fly, so when myspace times out (happens a lot...) Make Data Make Sense times out also. SO I pipe it into feedburner to get a reliable feed:
next I take that feed and give it to a WordPress plugin called FeedWordPress:
That plugin runs about every 30 mins from cronjob on on my server and imports anything new into my blog.
Now, having gone through all of that myself, I have to tell you that it may or may not be worth it. I find myspace to be quite possibly the worst site on the internet in terms of design and reliability. If I could find a way to make my WordPress posts go to myspace instead of vice versa, I'd be a much happier man.
You're question of going back more than 10-15 posts is not exactly solved by this, but once it's in your wordpress database you have full control over the data, so you can do what you want with it.
(And, if you're interested, I import my WordPress RSS feed into facebook ;)