Timo - I got some really useful advice on weaning from some health visiter booklets and there's lots of useful info on the net. Over 5 yrs ago, with ds1, I weaned from 4 months. Official advice is now to wean from 6 months, but after speaking to my h/v, started to wean ds2 from 4.5 mmonths.
According to h/v, the advice to wean from 6 months comes from the World Health Organisation (WHO), but that this doesn't take into account, different standards of food quality, accessability of different kitchen equipment ie fridges, washing detergent and so forth in the more developed countries such as the UK, so I was OK to start weaning from younger than 6 months. Kinda meakes sense I guess.
One word of caution: there's so much advice out there about weaning; it might be worthwhile, booking some time in with your health visitor with a list of questions (or someone else who's at a similar stage), nothing beats being able to talk things through; and finding one or two main sources of information and sticking to them. If you ask 10 different people, you can end up with 10 different responses leading to even more confusion. With weaning, I guess that there's some basic core principles which most people will follow ( again your h/v could be a good source of info). Once you're armed with the basics, then go out and get further info and use what makes the most sense to you and your baby. HTH