I created my rose collage of a few posts ago, with a great free program called Picasa which you can download here. It is a very easy program that gives you a couple of possibilies to make a collage and also to postwork them with all kind of effects like sepia!
If you have photoshop, there are some super actions and filters available to get a nice nostalgic look. But if you don't have photoshop, which is a fantastic program but costly, you could settle for Paintshop Pro which sells for 59 dollars and perhaps at Ebay even cheaper. I have PSP 7 and 11. I still use PSP 7 because I like the interface more than the one of the newer versions. PSP 7 sells for as low as 20 dollars at Ebay etc. Xero made some super filters for photoshop that also work in PSP and best of all they are free! They work in my PSP 7 version!
At the samples below I used the free filter Nostalgia. You can download them here!