Can anyone help me before I go insane???

I was given the 30Gb Ipod for my birthday. The disc supplied with it included Itunes version 6 and the ipod updater is 2006-06-28. I installed everything ok and purchased a number of songs and a video from the itunes music store. However I've been having multiple problems.

1. When I restart my pc it 'forgets' it's authorised to play files downloaded from the store. I have to log on and authorise the machine again before I can play the files on my pc or update ipod.

2. The music video I purchased copies to ipod and plays on it fine. However if I open the file on the hard drive in itunes it plays with no sound. If I open it in Quicktime it plays fine.

3 When I tried to add some other videos that were already on my harddrive I had all sorts of fun,namely:

Some files will not copy to the library. I click on 'add file to library' and select the video I want to add but it just refreshes the library without adding the file.

None of the videos that I did manage to add would download to ipod because they were in the wrong format. I understand that,but two of them were already quicktime files (.mov). Should you have to convert .mov files before they will play on ipod?

I then converted two other mpg files. When I updated ipod,one of them transferred ok,but plays on ipod with no sound. The other did not copy. I got an error message saying 'some files were not copied to ipod because your ipod software is too old. Goto www........to dowload the lates ipod updater'

So I go to the Apple website and find the link which is telling me to dowload and install itunes version 7. Did that,only it won't run! When I try to open it I get 'The application could not be opened. An unknown error occured (0x666D743F)'. 2006-06-28 won't run either as it just tells me that 'this version of ipod updater is no longer supported.You must now update using itunes v7'. Only as I 've said I can download version 7 but can't frigging get it to run! So I can't update my ipod software!

Sorry if this is long winded but can anyone make any sense of some of it and offer some hints as to what's going wrong?