Is it possible to wirelessly transfer my photos from my old Canon 5D (original) to my computer (macbook) over the internet? I have heard great things about magic SDs, but I only have a CF card slot. I don't mind getting creative with a Raspberry pi or some similar mini pc.
You can install a tethering app (Canon's EOS Utility included with your camera's software disc and free update downloads available from Canon is one such app) on anything that will run the correct OS. A small tablet or netbook running Windows, for instance, will let you connect the camera via a USB connection. Any Apple device that runs Mac OS X (original version) should be able to do the same thing.
If you choose to use EOS Utiliy, be sure to download it using the 5D support page, as the latest versions of EOS Utility no longer support the 5D. By using the 5D support page and designating the OS you are using on your device, you will get the last version that does support the 5D (ver2.7.3). The latest Windows version that is supported is Vista, so you'll have to choose that to get the EOS Utility 2.7.3 download. Even though there is no version of EOS Utility compatible with the 5D when Widows 7 is chosen as the OS, it will probably work with Windows 7. (I've found this to be true with other older versions of Canon software that had no version listed for an OS released after the Camera was no longer supported by updates). The last Mac OS that shows an EOS Utility download is OS X (with no updates). I do not know whether that version of EOS Utility will work on a later version of OS X.
Set up EOS Utility (or other tethering app, such as LR, if you can find a version that supports the 5D) to transfer images as soon as they are recorded. There are apps that allow you to tether cameras to Android or iPhones/iPads as well. The 5D may or may not be supported by these.
From there, it's just a matter of having the tablet/netbook/device connected to the internet via WiFi (or directly to your Macbook if it is within WiFi range) and using a file transfer app that will monitor the folder(s) you are saving the photos to and send them to the Macbook as they are created. In the past I've seen event photographers at large conventions roaming the room wearing a tethered tablet on a harness sending to their assistant in a sales booth at the venue over WiFi. Now that many higher end bodies include SD card slots I haven't seen a device tethered to the camera in a while.
Someone did this by putting a Raspberry pi into a 5Dmk2 battery grip, details here : http://www.davidhunt.ie/?p=2641
He uses gphoto on the Raspberry pi, according to gphoto's web site support of the original 5D is "Experimental" - so you can't know if this will work or not without trying.
Certain versions of the EyeFi can be used in SD to CF adapters in certain older model Canon cameras. It isn't officially supported, but it is reported to work by several on the internet. The first one I found for your camera was here and claims the Synchotech SD/CF adapter works with the first generation 4GB EyeFi card. Note that you need to avoid formatting the card while it is in the adapter and range may be reduced.
Alternately, you may be able to find a WFT-E1a used, though at this point it is probably more worth it to just upgrade to a newer model that includes wifi since the WFT-E1a appears to still run about $300 used.