U H F .

Jason, it could be that they are talking on Channles 30 onwards, as these are the same channels as the repeater channels, but without repeater access.

I am no expert though.

Make sure you have the duplex button turned on if this is applicable to your model. Key the mic when the repeater channel is quiet (ie transmit for a couple of seconds without saying anything) and if you are reaching the repeater you will see the RX (receive)light come on and probably hear a beep after you release the TX (transmit) button. By trying all t he repeater channels you can determine which is your closest repeater.

25 watts is the power level that most commercial radios transmit at. You're probably tranmitting at 5 watts now. 25 watts will give you significantly more range but definitly not 5 times as much. Technically, its also also illegal to transmit on CB frequencies at 25 watts. Other radios you are talking to may hear you but you may not hear their reply. It can be useful if you are a long way away from a repeater and the repeater cannot pick you up on 5 watts TX. But before you ajust anything, try the above.

Sounds like they gave you a 3db Rubber Dipole or somthing similar, great little arials and best for around town, big ariels are good for flat ground with line of site, small ones typically are better for around town. You can buy the cable and software for your Icom to programme scanning channels and commercial channels, you can also turn the CB channels 25watt option on. Yes it is illegal but plenty of people do it and if you are a responsible radio operating no one will care, it's only if you are a DH on the radio that people might complain.
But as mentioned in a previous response I would say you problem with repeaters is that you are on Simplex not Duplex. ie you are not transmitting on the repeaters "input" channel.

ie
ch 1 transmit, ch 31 receive
ch 2 transmit, ch 32 receive
ch 3 transmit, ch 33 receive
ch 4 transmit, ch 34 receive
ch 5 transmit, ch 35 receive
ch 6 transmit, ch 36 receive
ch 7 transmit, ch 37 receive
ch 8 transmit, ch 38 receive

When you select ch1 on your radio hit the "dup" or "duplex" button and your radio will automatically jump to the higher channel 31 when you transmit and jump back again to the origional channel to here the response.

Repeater channels are only from 1 through to 8 so you will only want duplex on when using these channels.
Your radio will remeber which ones you've turned it on on and will stay on until you turn it of, ie once you've turned it on on a particular channel you shouldn't need to touch it again.

Hope this helps! The Icom is a brilliant radio, you'll be more than happy.