This will be an easy singlespeed project if the rear wheel takes a cassette (not a freewheel).
Check that first, it is the case, you just need a singlespeed kit for the freehub (about £15) and 5x single chainring bolts to remove one of the front chainrings.
Once this is done, you can look at risers and other bits.
Gearing wise, I find 65 to 75 Gear Inches to be good around town - use this calculator to see what the GI will be before buy your singlespeed kit: http://sheldonbrown.com/gears/
This will be an easy singlespeed project if the rear wheel takes a cassette (not a freewheel).
Check that first, it is the case, you just need a singlespeed kit for the freehub (about £15) and 5x single chainring bolts to remove one of the front chainrings.
Once this is done, you can look at risers and other bits.
Gearing wise, I find 65 to 75 Gear Inches to be good around town - use this calculator to see what the GI will be before buy your singlespeed kit:
http://sheldonbrown.com/gears/