Sorry, even though I support the site, I've always felt the built-in uploader sucks. I use both Picasaweb and Photobucket interchangeably to store and upload photos, and link to them wherever I post online. Lately I've used Picasaweb more because it plays more nicely with my Eye-Fi card.
sorry...another failed attempt
If you upload to Picasaweb (from Picasa or any other way -- like I use Eye-Fi), just click on the picture you want to upload to select it; it will now be the large picture on your screen. On the lower part of the right-hand column, click on "Link to this Photo" which will expand with options. Select "Image only (no link)" and select the size you want from the drop-down. Then copy that link and either use the simple BB code img tags as JohnnyChance suggests, or if using the wysiwyg editor, click the image button and select the "From URL" tab, paste the link and de-select the "retrieve" box.
Yeah, I do it that way too. But sometimes you have to give all the real instructions. :D
Also, using the embedding link makes sure outsiders can't find a backdoor into your albums if you don't want them snooping around...