One thing that our twins have struggled with as a result of autism is fine motor control and hand strength, which impacts their handwriting. They were really struggling with forming letters and having the strength to write more than a few letters at a time. One thing that Cuddlebug in particular had a hard time with was putting way too much pressure on the pencil / crayon so he'd tear holes in his paper and wear himself out with just a few letters. During the summer before they started Kindergarten, we enrolled them in a handwriting group that was offered by their OT (this was in addition to their speech and OT). We knew there was going to be a fair amount of writing involved in school, so we wanted to help them prepare.
In Kindergarten they did writing time in the special ed classroom (they were in a regular ed class most of the time). Their resource teacher and OT used several supports that were helpful, including a slanted board and special pencil grips. We saw steady improvement in their handwriting as the year progressed, although they continued to struggle with it and weren't at the same level as their peers.
When they went back to school after Spring Break that year, we started to notice improvement in their handwriting. We realized that the only thing that had changed was, we'd gotten them each a Nintendo DS to play with on our trip to Texas to help keep them busy in the car. I know it sounds weird, but I've actually heard the same thing from other parents -- that they saw improvements in handwriting after their child got a Gameboy or Nintendo DS.
Playing with a handheld game like this requires repetitive small hand movements, which in their case built up their hand strength and helped them start being able to make smaller letters (they were known to write huge letters). By the time 1st grade started, while their handwriting still wasn't quite where their peers' was, they were writing smaller letters in straighter rows (not lopsided down the page), with smoother lines (not shaky lines) -- a significant improvement!
There are educational games in addition to the usual video games, so they get the benefit of those also. Obviously, we have reasonable limits on how much they can play, but it's nice that something fun has also been helpful in a therapeutic way :). So if your child is struggling with handwriting, consider possibly getting them a Nintendo DS or Gameboy to help build up the muscles in their hands and practice those small muscle movements.