huangmonkey,
first of all, SIA CAN'T take you in unless you are 26+ (for Singaporeans).
secondly, to cross over from airforce is not easy but i've seen many, and i mean many. the waiting period to be released from airforce is long but some for them chosed to quit airforce with one month notice, then apply for SIA direct.
one of the few differences between the options mentioned above are pay received during training. a difference of about 2k per month.
hope that helps.. go find out more about all these admin stuff from friends or thru instructors at YFC. if not mistaken, some of them were ex airforce instructors.
I too had a lot of trouble digging for aviation related information when i first started out. =)