Unable to do Software update, access iTunes, use widgets on dash and upload

Question

*_Here is the problem:_*
1. Unable to use Software Update. When I try I get: "+A networking error has occurred: timed out (-1001). Make sure you can connect to the Internet, then try again+" This is despite being connected to the internet and getting most things done.
2. Widgets which require data retrieval are not working. Notably weather and currency convertor.
3. iTunes cannot connect to the store. Tells me to check my network (which, if I do, I am told is fine, thanks)
4. Cannot view images (such as car rental vouchers) which are meant to display in email. In fact- the entire email disappeared before my eyes! But CAN, luckily, view on the server so I KNOW it is not just that the image is "spam" etc.
5. First thing on this list which made me wary- I cannot upload to YouTube, it times out ("unknown error" but timing out is mentioned) and this is using Firefox 3.8.3.
6. Safari will not load at all- it just keeps trying to load.
7. Displaying pages is slower than usual and downloading Onyx took ages and displayed no data regarding the file size or length of download time.
*_What I know:_*
1. I didn't update the last two times I was prompted because I was too busy to have it shut down on me and restart, etc.
2. I also had a go at trying to set up a web proxy and failed miserably. Though I actually changed the settings on another network to the one I am using I am so not network-literate that I fear that I have somehow done this to myself.
*_What I have tried:_*
1. safe starts, restarts,
2. deleting the preferences pertaining to Software Update from the various locations,
3. repaired permissions and-
4. thought of (I cannot afford to lose the data and haven't the time to back up just now- as per usual, this comes at the WORST time as I am on standby to fly out of the country due to VERY heavy and sad family affairs and need access to the files on the computer even if I cannot fully use the internet- just too many people/GB Pounds riding on this) using Onyx to try to "fix" this.
I have read up on others getting similar issues but am not certain that everyone has ALL the symptoms I am seeing (and then they may not be busy trying all these things on the one day and may not KNOW it is affected as well!). And I have tried each and every cure offered to these people. No good.

Answer 1

When you are going to be connecting to different networks that require different settings--such as proxies--you must establish different Locations in your Network System Preferences. If you're going to be connecting at college, you may want to set up a location called "College" and set the proxy settings so you can use it there. Then, when you want to go online at school, go to System Preferences -> Network and change your location to College. Then when you get home, change your settings back to "Automatic" or whatever you've named your home location.
Your Mac doesn't differentiate between networks it's connected to in order to automatically apply different settings. It relies on you to do that through the Locations set-up.
Anyway, glad it's working for you, and thanks for the star!