Do you need special permission to take your camera inside with these concerts? In holland they wouldn't be allowed probably. They are fantastic shots!
It depends. Large venues ( Sportpaleis Antwerp, Vorst Nationaal Brussels, AB Brussels), festivals and cultural centres require accreditations. The best way to go is to work for a webzine and have them to ask the photopasses. It often works, though the really big names (Pink, Metallica, etc.) remain unreachable.
BUT, in the summertime, there are lots of smaller venues around that are free and where you can take photo's without any problems. Just be in front. Great to learn the skills and build a portifollio. I also manage to get inside smaller gigs without the backup of the webzine, certainly if they see my site.
Mic, you won't regret the 50D, it's such a difference from the 400D. I still love that camera, but the handling and speed of the 50D are just something else. I doubted for quite a while whether to buy a 5D as upgrade, because it's about the same prices as the 50D, but by the time I decided, they weren't available anymore as a new model and second hand was not my intention. Still would like to see what it can do. The 5D MKII is overkill, even for me... lol