Yep! Remember, if you want to post a larger version of the picture in the thread itself, just be sure to copy the text link that Picasa gives you for the "800 px" (or whatever) variant of your photo!
You should be able to view your picture, select the (Number 1 in picture) "800 px" dropdown box, which will change the text that picasa gives you to link. (number 2 in picture)
Copy
that text into the tool, hit process, then paste the result directly into this forum and you'll have your 800px size (with link) picture in the thread!
Same for the other sizes. I believe picasa defaults to the 144px thumbnail size when you're copying the "link text" that it gives you.
Test from Picasa