My question is about Picasa 2 How do I zoom in ...

If you simply use their zoom feature - that won't change the image at all.  What you could do, if the image is large enough in terms of resolution, is crop the part you're interested in and since Picasa will still try to fill the screen with the newly cropped image - it'll look like you're zooming in.  It's just an appearance, since you didn't really change the resolution or anything else, just cut out a part of the image - but on the screen it'll look like you zoomed in.

 If you want to keep the original and the cropped version - you'll need to duplicate the original image before cropping it and then have 2 images, one cropped and one not.  Simply do the standard copy/paste (Ctrl-C and Ctrl-V combo) to create it. 

 Hope this helps.

It's not so much 'round about', it's more about what the software is for.  Picasa does have some nice editing capabilities, but its main purpose is to catalog and easily manage/view/print/email collections of photos, not provide extensive editing.  What you're trying to do is somewhat equivalent of someone creating a letter in Excel.  Sure, it can be done, but that's not the intent of the application.

 Also, zooming in isn't exactly an editing function anyway.  Graphical images (at least the ones you store in Picasa) are 2-dimensional beasts.  There is no information about depth and thus no zooming in or out in a sense of how zoom is typically done.  You can zoom in and out when getting ready to take a shot, but once you have it - there's no natural zoom in/out ability.  There's no information in the image for such action.