yeah picasa is a good option too. its available as a free download and its not that big...just get it from google. well ok this is how to go about it.
USING PHOTOSHOP:
open adobe photoshop. a box will come choose new file. choose the size to be the same as the size of the paper which u will print it on.
then make the window smaller. from windows explorer, drag each picture u want into photoshop. once all of them are there, u can make the window large again. then drag each picture into the position u want it to be in.
if u want irregular edges, take an eraser and make it how u want. ur done dont 4get 2 save
USING PICASA:
Use Picasa's "Collage" button to create one–of–a kind photo collages. You can even put your collage on a mug, apron, greeting card, even a mouse pad. Get started:
1. Select the pictures in Picasa that you want to appear in the collage. (Hold the Ctrl key down to select multiple pictures from different folders.) All of the selected pictures will appear in the "Picture Tray" at the bottom of the screen.
2. Click the "Collage" button at the bottom of the screen.
3. Select the type of collage and background image. For location, select "Current Folder" (by default, Picasa will save your new image to the currently highlighted folder). Click the "Create" button to finish your collage.
hope it turns out 2 b good