Ok, im sending this tool to Bendycat, its something I knocked up out of nothing but I found it worked a treat when I needed it. As Bobafett mentioned, it might be a good idea to keep track of this tool, as others may want to use it. I will explain how to use it on here instead of PM'ing people as others can then refer to it. I think it was quite simple, lol (it was 5 years ago)
Remove axle and bearings, place large rubber bush and steel smaller cup over the hub to be straightened. Insert threaded bar with one washer (Non-welded end) through the steel cup and bush and through the damaged hub. Now (this bit is fiddly from memory) You have to place the other washer and nut onto the threaded bar inside the hubbed area, it can be done. Once screwed on, take up slack with top (external) nut by hand. Then hold top (welded) nut with spanner or socket and place spanner on the nut you just tightened by hand. Now tighten this nut, it will be hard work but remember you are pulling the hub out at this stage. Sadly you have to just do a bit at a time and keep slackening the whole assembly to check progress. Thats about it, if you pull it out too much, whack the hub back in bit by bit with a lump hammer and a block of wood on the hub to avoid damage.
Hope this helps you all, (everyone will be buying knackered old mags now)
Link to my original post, pics here that should hlepl! http://www.radbmx.co.uk/forum/index.php'topic=3657.msg35859#msg35859