I went to Uni last year with 2 A levels and 2 As levels.
I fell asleep in my psych exam and decided to drop it in AS.
At a2 i picked up photography AS.
Some uni's accept them, some don't.
its best to call up Uni's your interested in now before making the deicison to see if they consider you when you eventually come around to applying.
Dont trust UCAS either with this, i applied to Derby Uni last year after UCAS told me they accept AS grades, however when i recieved an offer they refused to accept my AS or even acknowledge them. Luckily they only wanted 180 points, and i didnt go anyway
If i was you i would keep with the subject, full a levels are more respected and it can make it a struggle to certain Unis.
Although last year i was in luck, and Portsmouth, even after saying they didnt take AS grades stil considered them, and i was only rejected by Southampton Solent for holding 2 a levels only out of 5 choices.
This year, i was rejected by Plymouth and Coventry Uni because they wouldn't take my AS grades into consideration.
However, i got into Uni this year (2011 entry) with 2 A LEVELS AND 2 AS's, and have recieved 3 offers from Unis this year to also go onto courses with my grades.
Hope this helped