Their client is based on the math libraries of GIMPS founder George Woltman. Also, it is very likely that the project will never succeed - quite frankly, it is likely that some of the numbers to be eliminated will need to be tested further than present hardware can test in less than several months.
Also, they actually sieve far, far higher than 2,000,000,000. The reason is that it's possible to use special software like NewPGen to sieve an entire range of numbers at once. In particular, for the form k.2n+1 described above, a candidate factor can be compared to all the candidate prime numbers with a given k at once. This means that it makes sense to sieve into the trillions or quadrillions, since you'll still be factoring away a significant number of candidates. Google on "NewPGen" for more info.