Alex, don't over-complicate things. What you describe as big as a matchbox is the battery
The memory card is located on the right side of the camera (looking from the back) under a small door - very obvious to find.
Go out to Big W, Harvey Norman, KMart, Camerahouse etc and buy on of the CF card adaptors - see my image below. I have had this - obviously - for going on 15+ years, back when I had my first Canon digital camera. I also had a 300D, and used this with it, as the 300D uses CF (compact Flash) cards. I use it today with my Canon EOS 5D Mk II. I bought mine in Singapore for a whopping $2...
Just open the side port, remove the card (press the eject button with the camera OFF), insert into CF card adaptor (it'll only go one way, but don't force anything anyway), and plug that into a USB port on computer. The computer will do a first time install of the onboard driver for the adaptor (you need to do NOTHING except wait for it to finish - it does everything itself). Once it's ready, open the files from the pseudo-drive it creates in your drive list. Import the photos from there.
If you shot in RAW instead of jpeg, you will need to find the right DIGIC RAW codec for it (should be a DIGIC II from memory). Adobe Photoshop these days comes with Canon RAW codec anyway, irrespective of which type. If you shot in jpeg, every photo program should see it, including Windows inbuilt apps.
Using the cable attached to the camera is slow, and I have had issues that way previously.