Pixma connection to vista

I had the same problem but figured it out! For anyone else with this problem, here is the info I received from Canon:

In order to scan using the MP800, the MP Navigator program must be installed.
To download the MP Navigator for Windows Vista, please follow these steps to download files from Canon's website:
1. Visit Canon's website at: www.canontechsupport.com
2. Just below 'Please choose your product from the menus below:', select your model in the following manner:
a. Click the down arrow on the top drop-down box and select Multifunction.
b. Click the down arrow on the middle drop-down box and select Inkjet.
c. Click the down arrow on the bottom drop-down box and select PIXMA MP800 and click 'GO'.
3. On the Support page for your unit, click the 'Drivers & Downloads'
tab.
4. Click on 'Drivers / Software'. A new window will appear.
5. Select [MP Navigator Ver. 2.02 (Windows Vista)].
6. Read the License Agreement on the next page, and if you agree, click on 'I Agree - Begin Download' at the bottom.
7. Click on [mpnmp800win202ea13.exe] at the bottom of this page.
8. A File Download box should appear. When it does, select Save.
Note: This feature may not be available in all browsers.
9. When the Save As box comes up, choose Desktop. Click Save.
10. Once the download is complete, close all windows.
Double click the [mpnmp800win202ea13.exe] file on the Desktop.
Installation will complete.
If you have already completed these steps and you are still unable to scan, we will assist you in troubleshooting the issue, but we will need some additional information.
Is the scanner listed in Device Manager? To find this out, please follow these steps:
1. Click on Start.
2. Right click Computer and left click on Properties.
3. Click on the Device Manager link under Tasks in the upper left hand corner.
Is there an entry in the list named 'Imaging Devices'? If so, click the [+] next to it. What is listed under it?
Is there an entry in the list named 'Other Devices'? If so, click the [+] next to it. What is listed under it?
Click the [+] next to Universal Serial Bus Controllers at the bottom of the list. What is in the list under it?
Is the USB cable connected directly from the back of the scanner to the back of the computer? Or is the scanner connected to a USB hub or some other external USB device?
Is the USB cable plugged into a USB port on the back of the computer that is part of the motherboard or is it connected to an add on card?
Do you have USB ports on the front of the computer? If so, connect the scanner to one of the front ports. What happens?
Do you have a different USB cable that you could try?
Please, be as specific as possible and do not send screen shots or other images of the Device Manager as we are unable to view them. The more information you can provide to us the better understand we will have of the situation. We thank you in advance for your patience.
We look forward to your reply with the information we have requested regarding your Canon PIXMA MP800.
Thank you for choosing Canon.

Try a different USB cable, I did and it solved all the probs I was having with my printer. I could not scan back to the computer and with my new computer which I hoped would solve the problem, the computer would not recognise the printer but it said there was a device connected.

You need the vista driver for the printer, you can either download it from the support section of the website, or visit the service centre for support