Microsoft Picture Manager is an integral part of Microsoft Office and not available separately. There are loads of far better free programs available anyway.
The free image viewing and editing program which deserves a place on everyone's PC is Irfanview:
http://www.irfanview.com/
Google's Picasa software is also popular and, like Microsoft Picture Manager, has a built-in facility to upload images to online galleries:
http://picasa.google.com/
Serif PhotoPlus SE is an excellent (and totally free) photo-editing program:
http://www.freeserifsoftware.com/software/Phot oPlus/default.asp
If you want the flexibility that Photoshop offers (but for free), you'll need GIMP. However, just like Photoshop, it takes a bit of study in order to get the best from it:
http://www.gimp.org/
Chris