good place to start is:

http://www.ge.ch/moe/uk/procedures.asp

Taxes are a disaster  (in Geneva that is) . Use a fiduciare (think there are even some members here who are or who know a good one).

Normally the procedures for work permits are quite straight forward as a member of the "old" EU members, it doesn't hurt to give them a call, most of them speak english and are quite helpfull and friendly.

Good luck!

If you're an EU citizen, getting a work permit is a simple admin process. Don't spend money on a lawyer, just use the link Martin shared and do it yourself .

Then, unless you make less than CHF 5K a year (or something like that, I don't know the exact number), you need to register as an independant with the authorities, for tax reasons. There you might need to use some help. Any accountant will be able to do that for you.

Whatever you do as freelancer (in the legal sense of the word) you need to first clear your position with the Social Security (AVS). You need to apply for the independent status, provide docs, business plans etc. Get in touch with this administration to inquire about current requirements.

http://www.bsv.admin.ch/kmu/ratgeber/00496/00557/index.html?lang=fr

If, they agree, you can freely go out and shine as a freelancer. 

Now if you decide to disregard this requirement (as many do), you have actually little real risk of any damage.

BUT! if one of your customer gets audited by the social security and they find out they paid you without verifiying your independent certificate, they will seriously charge the individual/company, possibly for fraud, quickly followed by the other social insurances that will also want their share of the money... 

I 

Thank you all, I will look into these links...