how far is HKIA (hong kong international airport) terminal 1 to terminal 2?

T1 and T2 are linked by a central access way and by covered walkways at either end. They are within two-minute walking distance.
http://www.hongkongairport.com/eng/passenger/departure/all/check-in-departure/airport-check-in.html

And since you are using another airline at terminal 2 to go to Singapore, I'd expect that you will have to check in to get your boarding pass. You might confirm this from your agent, because at no time I have boarded an airline with the printout of ticket.

directions inside the HK airport is pretty clear. E1 zone should be the transit area 4 everyone. guess u probably needn't leave the restricted area n walk to T2 urself. they should hv shuttle to drive u there. but if u really needed to walk there.......T1 & T2 r linked. walking time just 10 mins. but not including Q up at the immigration. s'time it might take long if the Q is long.

no need to worry abt it .It's not to far it will take abt 15-to-20min

Why ask here? You might get a false answer to bring you to the wrong area. Best is to check with Travel Agent even if you didn't buy from them the ticket. If not, check with Jetstar. Where did U get the info of HK with 2 terminals?

I am not familiar with transfers at HKIA. But in regards to terminals, as soon as you get off the plane, you'll be guided to the trams, which will take you back to Terminal 2. It's fast (I believe the tram comes every 3-5 minutes). Just follow the signs at the terminals and you'll be fine. For the connecting flight, you will need to ask the staff at the ticket counter (before you leave) and if they can't give you your next boarding pass, you can ask the ground staff at the HK airport - they are everywhere so you don't have to worry about that either.

If you are afraid that you're running out of time, just let the ground staff know you need to rush to your next gate and they will help you. One thing I like about HKIA is everyone works fast, from ticket counter to security people, etc.

Have a safe trip!