I have a comparison of the DIana+ and Holga on my website:
http://dianacamera.com/archives/50
The DianaF+ has a flash, so that the main difference between the two cameras is that the DianaF+ is a little more flexible, but at a price.
The DianaF+ will cost $100US, while you can get a Holga 120N for $25US.
Photo quality is very similar with the 2 cameras:
Holga
http://www.flickr.com/groups/86881528@N0...
Diana+ and F+:
http://www.flickr.com/groups/diana_plus/
If you are new to film photography, my recommendation is to get a Holga. The lower cost will allow you to experiment with plastic camera photography without having to spend lots of money. If it turns out that you love working with the Holga, and want the flexibility of the Diana+, then you can spend the extra money knowing what that it is well worth it.
Holga:
Freestyle Photo Supply
http://freestylephoto.biz/
$25, but without the pretty box and book.
At Lomography.com:
Diana+ - $50
DianaF+ - $100
120 film takes a little work to find a lab that can process it for you. If this seems like too much trouble, you might consider the 35mm Holga 135BC. While I prefer the large square negative I get from my Dianas and Holgas, 35mm film is easier and cheaper to deal with. You can find a local 1-hour lab that can process and print the film for you, and in many cases, scan the film negatives in for you so they can be used digitally to upload.
Lomography? It's just a way of classifying toy camera photography. The folks over at Lomography have been hugely successful making toy camera photography into something of a phenomena, but I dislike the term as being too limiting. I'm a photographer who uses some low-tech plastic cameras along with other cameras.
Film? Film is beautiful. It has a dynamic range that can be matched by very expensive digital cameras, but for a few bucks a roll and cheap plastic camera, can be yours. You don't have to use low tech cameras to get beautiful images. It only requires a good eye and feel for composition.
You can find lots of great Holga tips at these websites:
http://www.squarefrog.co.uk/
http://goholga.com/
Then there's my own website:
http://www.dianacamera.com/
I have lots of tips, tricks and photos taken with both the Diana and Holga.
I also have several how to videos for both the Diana+ and Holga posted at youtube.com:
http://www.youtube.com/user/kaituba
Good luck!!