I am a regular visitor to Prague, your hotel in certainly in the Old town. you could get the AE bus to Namesti Republicky and you can walk to the hotel in a couple of minutes from there but I have used that bus several times and it can be a bit of a Zoo and very crowded .A private shuttle would cost around 600kc and take you directly to your hotel in comfort.
http://www.praguetransport.com/
I can highly recommend this company, I have used them several times over the year as have family and friends. Run by an American ex-pat and his Czech wife, all the drivers speak English (actually many are British and American).

as to times .depending on traffic /time of day I would say 40-50 minutes by bus and 30-40 by private car/taxi.

Laurieco, I have also used the private shuttle recommended above by unclegus and was very pleased with his service. For me, when I'm jet lagged after over night flight the last thing in the world I want to deal with is public transportation so I always opt for good alternatives.

Hi unclegus and Louisa, I reserved a car last night with http://www.prague-airport-transfers....ivatetaxis.htm

I got a confirmation from them immediately and an email several minutes later. I didn't have to prepay so hopefully they will show up! Thanks for the help though.

HI laurieco, Prague is a wonderful city...we were just there in April. We used the prague-airport-transfers company and they were great! Waiting for us at the train station with a sign, took us directly to the hotel in Old Town...no worries at all. I had also booked them for friends that were meeting us (coming from the airport) and they, too, were very pleased with the service. Another thought...we did a Taste of Prague tour w/ Jan and Petra...fabulous evening, delightful guides, great food. One of the highlights of our time in Prague. They need to be prebooked, I would think, but you might look into it.