I've never used Picasa before and when I ran it after install, it looked like a decent image viewer (and editor) to me. It was indexing all my mounted volumes for images, which is probably why it's at 100% usage when you launched it.
As far as the full screen, I ran a slideshow view in Picasa and it full screened the images for me (fit to screen without scrollbars) and I could use the arrow keys to move back and forth.
Again, I've never used Picasa up until 3-4 hours ago just to prove Picasa 3 would work in Ubuntu 9.10, so I'm sure there are probably other ways to do what you want to do if you take a few minutes to play with the program or read some man pages.
Anyway, sorry it doesn't work out for you. Worst case you can try to use WiNE to launch that ifranview app.
As far as the full screen, I ran a slideshow view in Picasa and it full screened the images for me (fit to screen without scrollbars) and I could use the arrow keys to move back and forth.
Again, I've never used Picasa up until 3-4 hours ago just to prove Picasa 3 would work in Ubuntu 9.10, so I'm sure there are probably other ways to do what you want to do if you take a few minutes to play with the program or read some man pages.
Anyway, sorry it doesn't work out for you. Worst case you can try to use WiNE to launch that ifranview app.

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