If the 25s are full you can get a 49 and walk from moulsecoomb.
From the trafalgar street walk up the hill & get the train = simples.
I am sure that I caught either the 28 or 29 to The Swan.
Brighton Hove Bus and Coach Company
A map of bus routes: http://history.buses.co.uk/bustimes/areawide.pdf
The 23 comes down elm grove onto lewes road and up to the universities if you don't mind a little walk. Route 23 Info
The 25 goes by the far side of st peter's church (far side from trafalgar street) Route 25 Info
The 28 and 29 stops in the university Route 28 Info, Route 29 Info (These are limited stop buses, so won't stop at every bus stop like the 23, 25, 24 or 49)
The 24 goes up coldean lane, if you get off at the bottom it's about 10-15 minute walk to the stadium Route 24 Info
The 49 stops at the far end of moulsecoomb way, not too far from lucraft if you don't mind a 10-15 minute walk to the stadium Route 49 Info
Which could involve waiting in a queue for 45 minutes , the best option is to catch a 25 from St Peters (the last 2 of the bendi-buses sent away for conversion and re-livery will be in service soon)