Sven,

You have a couple of options. My personal preference is Dynazip from Inner Media Inc. it has worked reliably for a long time.

www.dynazip.com

You could also try the Xceed zip librarys, I have no experience with their technology but it gets good reviews on a regular basis.

www.xceedsoft.com

I believe theres also a download or two in the downloads section of UT that may provide this functionality?

HTH
Neil