The '05 bikes don't have adjustable suspensions. Otherwise, tires need replacing. I like the Kenda K671s, they're inexpensive and last really well. There's a nice section on tires over at
http://forums.ninja250.org/ , look in the FAQ.
I got my '06 in '09 with only 2k miles on it, the tires were junk and had to be replaced ASAP.