Advice on competition swimwear commencing January 2010.
Here is the latest approved swimwear list from the FINA site published on the 4th Jan 2010.

This link takes you to the FINA website and the page showing permitted Performance swimwear from Jan 2010. This relates to the material composition and coverage of 'Performance' swimwear
Swimwear that is not primarily aimed at enhancing performance is permitted but must still comply with the regulations below relating to coverage:

BL 8 SWIMWEAR
BL 8.1 All FINA approved swimwear to be used at the Olympic Games and FINA World Championships must be approved by FINA at least twelve (12) months prior to the start of the respective competition. In addition, it must be available for all competitors by 1st January of the year of the Olympic Games or FINA World Championships.

BL 8.2 In swimming competitions the competitor must wear only one swimsuit in one or two pieces. No additional items, like arm bands or leg bands shall be regarded as parts of a swimsuit.

BL 8.3 From January 1, 2010 swimwear for men shall not extend above the navel nor below the knee, and for women, shall not cover the neck, extend past the shoulder, nor shall extend below knee. All swimsuits shall be made from textile materials.

These rules apply at all competitions swum under fina rules.

So, 'jammers' are ok, and girls' suits can extend to the knees with racer-style backs.