I never really cared about how "valid" my html code was (as long as it works, no?), but now I have to for school... and it has to be Strict XHTML.

Like it's not enough that tables are absolutely horrible to figure out in Strict XHTML, someone decided that target="_blank" isn't valid anymore?!? Apparently, the reason is the W3C's Guideline 10.1:
Until user agents allow users to turn off spawned windows, do not cause pop-ups or other windows to appear and do not change the current window without informing the user.
Pfffttt... What's funny is that the "solution" to this problem you'll find all over is JAVASCRIPT (apparently, the W3C Validator will validate the script as strict XHTML). Every time I want a target to open in a new window, I have to use JAVASCRIPT??? And that's better than target blank how?

Is this really where web design is going?