There is a short review here
http://www.cameras.co.uk/reviews/canon-ixus-70 .cfm
The camera takes SD cards so make sure you buy an SD card and not any other type.
It says it comes with a 32Mb memory card, but that will only hold about 10 pictures.
There is a little chart here showing how many pictures you can get on each size of card. The chart only goes up to 6 megapixel and the Canon is a 7mp so it will be slightly less for your camnera.
http://www.digitalcactus.co.uk/memorycards.cfm
So a 512Mb card will hold about 160 pictures and a 1Gb card will hold about 320 pictures (these figures are a rough guide as each picture will be a different size).
You can probably get an SD card larger than 1Gb.