Thanks for the positive comments guy's, here are the basics on how to do the conversion.
the mods to the torches involves :
disassemble torch into 3 main parts (end cap with switch, main body, and LED/lens unit). cut approx 55mm of main body with good hacksaw, making sure you do not damage threads for lens unit.
dissasemble LED/lens unit and you will see that there is a small inbuilt current regulation circuit, unsolder this and run 2 new leads from LED module.
using the wonder of the web, do a search on 'dealextreme' for the mounts shown, they are a tight fit on the body of the torch, but with a bit of persuasion they wil fit. For the driver cards I went for some cheap 700mA fixed output types from ebay (look under seller 'sureelectronics').
I decided not to use the existing switch module, and simply got some suitable blanking plugs to fit the cut end of the torch bodies, the ones I found are plastic units that are commonly found at most electronics suppliers. these were then centre drilled and fitted with some simple and small waterproof on/off switches from Maplins.
Wiring is fairly simple - from the 7.2V battery pack I am running the 2 light units in parallel NOT series. the drivers need to be wired up with the +/- output to the appropiate wires of the LED's.
the negative (-) lead of the battery is run to the negative (-) input terminal of the driver cards, the positive of the battery is run up and through the switch units and then to the positive terminal of the driver card input.
the tricky bit really is getting the driver card and wiring all inside the cut down body section as space is a little tight. the wiring that passes out to the battery pack goes through a waterproof gromit mounted under the bracket assembly to keep it out of direct water spray.
the battery itself is mounted in a nylon fabric holder that mounts via velcro straps to the frame top tube. these holders are found on ebay as accesories used by 'airsoft' enthusiasts.
rough breakdown on prices are :
2 x tesco C-cell torches : £22
2 x mounts from dealextreme : £3.50
2 x driver cards from ebay : £11
2 x switches from maplins : £4
odds n sods (blanking plugs, wire, etc) : £3
battery pack holder from ebay : £4
battery packs can be got from ebay for approx £18 - £24
hope this helps a little, but any more questions let me know
cheers - UZ