Your gif pics need to be same pixel size. You can do this with Irfanview [free and much loved proggy].Or
click here GIFWorks will do it for you online. But your Santa will still be too big. If you are doing this for an xmas card in OE you can create stationery using the falling snow and then put an in proportion Santa where you will in the email. Gifworks also do a wonderful variety of moving scripts here click here -have fun!