“Error: file not found”, no post links (posts ok @ index page & dashboard side)

Here are a coiple of links as examples”
http://www.nationalplatform.org/wordpress
Shows the latest few posts fine, and all the category, page links;

http://www.nationalplatform.org/wordpress/about/
Single page I have;

http://www.nationalplatform.org/wordpress/2008/04/12/12042008-quotable-quotes/
Latest post;

http://www.nationalplatform.org/wordpress/2008/04/
Typical category;

Everything seems fine posting on the dashboard side; I can access all the different posts and categories.

And just a few examples of the posts dashboard side (the last two I can’t access via the website links):

2008/03/07 [07/03/2008] What Your Vote on the Lisbon Treaty Will Really Mean admin Lisbon Treaty No Tags
0
Published
2008/02/15 [15/02/2008] WHAT THE TREATY OF LISBON DOES admin Lisbon Treaty No Tags
0
Published
2007/10/18 [18/10/2007] Government should set up the statutory Referendum Commission well in advance of the referendum on the new EU Treaty to ensure citizens are adequately informed admin Uncategorized No Tags
0
Published

APPARENT FIX TO THIS PROBLEM:
Ok, I hadn’t come up with anything through the search words option, but then tried under the “Installation” Forum (hadn’t thought of this before, because I’d thought the installation went alright). The Thread is called, and located at:

“Upgraded to 2.5, now pages don’t display… WTF?”
http://wordpress.org/support/topic/164360?replies=71

I didn’t understand a lot of it, but for those of you who are having this problem, and who like me who have no formal training in, or deep knowledge of computers, here we go…:

THE COMPLETE NEWBIE’S FIX FOR POSTS THAT DON’T LOAD IN WORDPRESS 2.5:

1) Log in;
2) On the “Dashboard”, wander over to your top right, where it says “Settings, Plugins, Users”, and Click on “SETTINGS”;
3) Now wander over the next page to Click on “PERMALINKS” (this will be one of several options probably listed over the title “General Settings”);
4) You should now see the title “Customize Permalink Structure”;
Under this, there will be little buttons beside a list of options;
There are now two options to fix the post/page error:
a) – Click the “DEFAULT” button;
– Click on the “SAVE CHANGES” link near the bottom of the page;
(this will mean that the URL’s/Web addresses of your posts will end in something like “?p=123”); OR
b) – Click on the button of your preferred option (you should see some code pop into the box beside “Custom”;
– THEN Click the button beside “CUSTOM”;
– Now, in the box beside “Custom” and right BEFORE the string of code that’s in there, insert what’s BETWEEN these quotation marks: “index.php?”;
– Click on the “SAVE CHANGES” link near the bottom of the page;
(This will give you an URL/Web address for each of your posts almost the same as your preferred option, but just with “/index.php?/” preceding it).

This seems to work; although there is apparently some fix that you can do that removes the “index.php?”, I must confess I don’t really understand how it’s done; I will leave this thread open a bit longer in case any of you more advanced people wish to explain it (hint: imagine that you are playing with “mechano” sets, whereas I am still playing with “duplo” bricks (“Lego” bricks being too small and fiddly…)).

Thanks in advance, and hope this is of some help to someone else.