Well if you have a static link that your gonna use just use the 'Link' core control.
Here's what you want to do as an example:
- create sample xpage
- Drag 'Link' core control to xpage
- in properties window for link select 'Link type' as Open Page
- Select your page
- On the Window Behavior select 'Open New window or tab' option
Now with this there are some limitations, like only opening an already available xpage. But if you look at the source of what you just completed it looks just like mine.
<xp:link escape="true" text="Link" id="link1" target="_blank" value="/somepage.xsp"></xp:link>
I've played around with the source and cant get it to open a link that is external to the database so you would be left with using a computed field and placing the good old href tags in the advanced bindings. See my reply to the iframe thread for an explanation.