OK
Your website is made to a certain width.. its not flexible.. it stays exactly at that width...
If I come along wiht a smaller browser window than your website then i cant see the donate button (important) hence why design wise all the real important stuff on a website is usualy located top left to guarantee being seen by any size browser on any platform.. hand helds etc.
A lot of people will click a link to your website and a smaller window will open.. not everyone has tabs or a multi million pixel screen
I'd take that a couple of stages further.
The primary reason for the site is to raise dosh, and yet the only real indication is the donate button up on the top right, which is out of one's natural eye line.
Move the donate button into either the banner section, or give it's own widget panel above the Search Box and Sponsors box on the right.
You also need a page that shouts 'Give Me Your Money Now', linked to from every page and in the menu section. Call it 'How You Can Help', 'How to Donate' 'Give me your Dosh You Ba^&*ds', it doesn't matter; but that page HAS to be the easiest to find on the site.
- edit, I've just found the page and it's accessed via the donate button, which I assumed would take me off to a just giving page........ get my point?
You need to have a bit more punch in how you are selling your trip. I would suggest a page called 'Route' or 'The Journey' or something similar, separate from your about page; keep that for some details about who you are and why you are doing it. Even if the exact route isn't planned yet get an image of a map mocked up with your route highlighted on it, which will emphasise the effort required to anyone looking. You should also, if possible, put a thumbnail sized version of that onto the banner to push the point home.
The 1300 miles part is good, it makes it sound strenuous, but also include a time scale (ie 1300 miles in X days) and as you are going to be crossing the Alps at some stage emphasise it; what is your max climb, how many times will you be 3000 feet plus etc etc.
A good example of some of the above is here:
http://www.helpforheroes.org.uk/bbbr_2010.html
Talking of Home, I'd change your home page. At the moment it's the WP default Blog (& delete the Hello World stuff asap!). If you are going to Blog, that's fine and probably a good idea, but make that a page that people have to go to second. Your Index Page (ie the one that people get when they arrive at the site) should have a very brief description of what you are doing and for who, a medium sized copy of the route map, and a gert big F Off link to your donation page, it's your first contact with your visitor and you need to get the point across very quickly and simply so that you cater for their attention span. Too much text and they will wander off, save that for the more in depth pages, tell them what you are doing, show them a pretty picture and tell them how to give you money; if they want more they can read the rest of the site.
On the Sponsors page, when you are naming them at least provide a link to their website and possibly their logo as well, in addition to the Sponsors box on the right.
If I think of anything else I'll post it.
One last bit....
Make the DONATE page obvious, and repeat it everywhere! 
