BMW offers two kinds of warrantees; extended maintenance and extended warrantee. A lot of people get them confused. They both extended coverage to 6/100. However your BMW must still be under it's original 4/50 coverage.
The service warrantee is an extended service contract that extends the original "free" service coverage and is fairly comprehensive. It retails, depending on model, $1500-2500. The extended warrantee is only available to the original owner and extends most of the new vehicle warrantee with $50 deductible per visit. It retails, again model dependent, $2500-4500 or so.
In the spirit of disclosure, I currently have the extended service warrantee on my M3. I purchased it at a dealer I don't normally deal with because they give me the best price, MSRP, before the price on all BMW warrantees increased on June 16, 2007. In my case, $1195 seemed like a bargain considering the cost of inspection 2 and a brake job. However, at $2000 (new price) it may be worth looking into an independent shop for service. I plan on purchasing the extended warrantee sometime next year.