Du musst als Zielrahmen _blank angeben.
Folgende Standardrahmen gibt es:
_top: the document will be opened in the full browser windows. Use _top to open the linked document in full browser windows.
_self: the document will be opened in the same frame. Example, if I specify "HOME" on the left frame as "_self", the home page will appear in the left frame. (pretty ugly, huh?)
_parent: the document will be opened in the current windows' parent. Example, if there is a link in this right frame and it cause nested frame. Within the nested frame, I specify the link as "_parent". When you click that link it will appear back into this right frame and nested frame will disappear. NOTE: If there is no parent exists, it will acts like "_self"
_blank: the document will be opened in the new browser windows. Browser will launch a new windows while your previous page, which is the frame page, is still open.
Andreas