To answer your 2nd question 1st...no, you can't establish residency there before you get a job. :( In order to work there you will need a visa AND a work permit, and you have to have both before travelling there to start work. (or they will refuse you entrance) Also, your future employer is the one who has to apply for the permit, on your behalf.
There are 5 basic ways to live/work in England....
1. Highly Skilled Migrant Programme: for "successful people with sought-after skills." For example, those with a Bachelors, Masters, Doctoral degree, etc... you do not need a work permit for this scheme.
2. If the job you qualify for is a "shortage occupation'. The employer doesn't have to advertise for this in advance, and may simply apply for a work permit on your behalf.
3. If the job you qualify for is NOT a shortage occupation, the employer must have already advertised for the position and be able to show that they were unable to fill the position with eiher a UK resident or a EEA National. (nearly impossible lol)
4. Go to school there, and you are allowed to work part time.
5. Marry a Brit! lol You can work all you want!
So basically, you need to figure out what it is you have to offer the country lol....hopefully it is on the shortages list. ;) That seems to be the easiest way to do this, and the most beneficial to the country.
Good luck! And here are some links that may be of use!
www.workpermit.com
www.ind.homeoffice.gov.uk
www.globalvisas.com
www.ukvisas.gov.uk
and to find more information from those that have 'been there, done that', try:
www.uk-yankee.com