How to see my Picasa albums offline? In other words how to download a picture from my Picasa album to my sdcard? I can see in the gallery but not have it in my phone :( so I cannot see when I don't have wifi. I don't want full sync but I want to save a pic which I see in gallery easily.

Update:

I have a good picture in my picasa web album.
When I am at my home with wifi, I can see the picture, show it to others. When I go out of wifi connection, If I try to see the picture I wont be able to because the image which was cached will be deleted and no longer available. I will just be able to see the thumbnail. Alternatively If there is an option to save the image to sd card in the gallery image viewer, I will save that particular picture to my sd card when I have wifi and view it anytime anywhere. So now, If I want to download a particular image of mine from picasa, I need to go to internet->picasawebalbums, browse for the same photo I can see in gallery and then download it. Is there a simple way of doing this? May be with anyother app? 

Else, If I can access the cache folder where gallery caches picasa photos, I can copy from there. But I'm not able to find that too.

My phone model: Samsung Galaxy S LCD I9003

Update:
I found this app useful and allow me to save my photos but I cant browse friend's albums yet.
You can sync Picasa albums to the web via a setting in the software on your computer. Google gives you a little storage for free. 

Then on your phone you under Settings->Accounts and Sync, select the Google account and tick Sync Picasa Web Albumns.

Next time you open the Gallery app, it will show all the photos that have been uploaded to the web.