I don't know why you're having trouble downloading any of those files because they're attached on our server. Even the basemap is in 3 RAR parts on our server too. Maybe your browser's ad blocker is interfering or you have a third-party antivirus software which is overly protective. Maybe just try QuickCure3 first, it's universal and very simple to use as it doesn't require the original device firmware at all. Being a relatively small file, i've made a folder 'pack' for you with both the correctly named RGN file and Updater.exe and uploaded in a ZIP file elsewhere so you shouldn't have any difficulty downloading it. The link to it and a 'how-to' are behind the spoiler. If it works (doesn't always) you won't need to make Cure3 firmware at all. Seeing you said you're not 'a pc whizz kid' I've been overly pedantic in the how-to to be sure you get it right.
Spoiler:
Click this for download: [Only registered and activated users can see links. ]
How to use:
  1. Ensure you have [Only registered and activated users can see links. ] loaded to the PC you intend to use;
  2. Extract the "QCure_for_zumo_590" folder from the downloaded ZIP file to a convenient place, like the desktop where you can easily find it;
  3. Open the folder and drag 179601000330.rgn file onto the Updater.exe file which will open it's Graphic User Interface window, then select the radio button next to "USB Device" on Updater's GUI, leave it visible;
  4. Ensure the zumo has no media card in it and is completely OFF. You may have to hold the power button down for an extended time (10 to 30 secs) or remove the battery for a few seconds to turn it off;
  5. Connect a 'known-good' USB cable to the zumo, but not to the PC just yet;
  6. Put the zumo into pre-boot mode by appropriately holding the screen (probably top left corner), then maintaining pressure on the screen (easier to hold the zumo in your left hand using your left thumb on it's screen which allows your right hand to be completely free) connect the cable to a REAR USB2 port of the PC (don't use a front port or a hub or a USB3 port), that PC connection will power the zumo on into pre-boot provided you keep holding the screen firmly which might then show "Loader". Now immediately get your attention back to the GUI;
  7. Keeping the firm steady pressure on the device screen, watch the window adjacent to "USB Device" on the GUI then press "OK" on updater's GUI immediately you see the zumo's details appear in the window. Keep holding the screen at least until "Software Loading" or similar appears on the zumo's screen or preferably hold until the flash finishes. Updater will report success when finished;
  8. Don't disconnect the USB cable. Check that the device had now entered mass storage mode and is visible to the PC as a removable drive.
  9. Use RMPrepUSB to correctly format it in FAT32, carefully ensuring the correct settings are selected as described in the post: [Only registered and activated users can see links. ]. Then create an empty Garmin folder in the root of the zumo's flash drive;
  10. Disconnect the device safely and it should then boot into the normal mode but may complain about missing maps etc.;
  11. Reconnect to PC and run GarminExpress to replace any available missing files and then add the basemap.

If it doesn't work then you'll need full Cure firmware made from the device's firmware which we can walk you thru so no problem there, just a bit more complicated. Don't worry, this device is fixable unless it's got a physically damaged flash which is highly unlikely.