I'm thinking about buying a Canon XLH1 and own already the XL2.
I'm just wondering if i still can use the lences for the XLH1 that i used with my XL2.

My point is do i have to buy everything new, or can i still use them and what is the impact on the quality.

Yes, you can use your old lenses with the new XL-H1.

Canon said the old lenses wouldn't give enough resolution for good HDV results, but some people here have posted that, although a bit soft, they still get good results with their old XL-lenses.

Maybe I'm wrong, but from what I've seen so far, the 16X and 14X manual lenses seem to match, or even exceeds in some instances, the results taken with the new HD 20X lens.
I've got a feeling that it would probably be difficult for people to watch a HD screen and pick out the different footage taken with all three lenses if you wasn't told beforehand which lenses were used for each section.