Picasa 3 is free downloadable software (from http://picasa.google.com/) which lets you manage and manipulate your photographs. You can apply several effects to each photograph, you can resize, crop and create collages , slideshows or videos.
You can create large posters to whatever size you wish from your photograph which prints on the paper in your printer but overlaps to let you piece it together at the larger size.
You can batch export a whole group of photographs to a folder – handy when your digital camera produces high-quality large filesize photographs and you need to quickly resize a whole group for putting onto a website or blog.
You can create a video slideshow with animations and transitions along with audio.
Picasa’s own helpguide and tutorials can be found here: http://picasa.google.com/support/bin/topic.py?topic=14609&hl=en
See the following for answers from TechEase to several Frequently Asked Questions about using Picasa:
http://etc.usf.edu/techease/win/images/ – this also includes other helpful information about digital images in general.
Video tutorials on using Picasa from LearningElectric.com can be found here:
Resize multiple pictures for use on a website or blog by using Picasa – here’s how
Excellent introductory video to Picasa 3