There a 3 versions of the wii @ the moment,DMS, D2A & D2B the most recent one being the "D2B" produced in Feb 2007 onwards.
You can generally use your Wii serial number to check your version, or use this site to do it for you..
Nintendo-Scene Wii Serial Tracker
DMS and D2A versions are a piece of piss to chip and you could even program ure own chips if you had a programmer that costs around a tenner using a pic12f629 chip and the yaosm program code, or simpler still just buy one of the shelf.
The latest chip is the D2CKEY whic will work on all models but is a complex install on the D2B wii and best to get somebody else to do it.
The DMS and D2A versions of the wii can use any chip really and can be fitted within 10 to 15 mins.
these guys are pretty reputable and also do a fitting service (click on the nintendo wii menu )
Cyclo DS Memor 32 CycloWiz WiiKey WiiD Buy Wii Mod chip PS2 Swap Magic Coder V3.8 & Slimtool MK2 . Nintendo DS M3 DS Simply CycloDS Evolution
or if you have a local computer fair like Bowlers in Manchester then take it there and they will chip it on the spot, the pricewill vary depending what version wii u have so check the version b4 u take it.
for lots more information and the various types of chips then go here as its probably the best chipping forum on the net for info..
Wii Modchips - PSX/PS2/PS3/Wii Scene & Newz Forums