First of all Swindon is a hole and the sooner you leave the better.
Parking is there but if you want street parking then leave yourself a 20-30 minute walk which didn't and doesn't bother me. Closer to the ground you can pay for parking if that's your choice.
I normally use the fire station by the magic roundabout. Don't mind giving them a few quid and it avoids having to actually use the roundabout! Chippy opposite as well for after the match.