Most independant retailers will do it for you for about 50 quid!!!
1. ask around at work/college etc someone will have had it done. See if they reccomend a place that does it.
2. When you take it in take note of your serial number, you do not want an old botched machine back!!!
3. Get them to show you it working in the shop.
Thats about it if you are in the Yorkshire area I can reccomend someone who does it, or give you the contact details, as he takes in posted machines, but th ebox ways a tonne!!!
I chipped mine myself, took about 20 mins, 5 mins to solder and 15 to take and put the machine back together. Don't have any experience of soldering myself so I suppose anyone can do it. The chip I used was the Xecuter, one wire to solder and several big points which were quite easy.