Please understand that I am relatively new to JavaScript and if I give an explanation that is misleading I would hope that somebody would correct it for us.
The file was in a completely different folder is key here.
The "
\" is the escape character in JavaScript.
for example, if you wanted to display double quotes inside of a string that is already inside of double quotes you would have to use the escape character. The "\" is ignored so the character that follows will be displayed
"Hello "JavaScript"" // This code would NOT work
'Hello "JavaScript'" // Hello "JavaScript"
"Hello \"JavaScript\"" // Hello "JavaScript"
The "%20" is the code that represents the space between words. A computer only will see numbers. Everything you type in is changed into a number so that your computer can read and process it. It is displayed back to you in a different format so that you can read it. The number "20" is the hexadecimal character code for a space.
C:+---My Documents+--MyWeb+
| | |
| | +--here.html
| | |
| | +--page1.html
| |
| +--JavaScriptGoodies+
| |
| +--thanksalot.html
+--New Folder+
|
+--New Page.html
To go from C:\My Documents\MyWeb\here.html to
C:\My Documents\MyWeb\page1.html
href="Page1.html" (in the same folder)
To go from C:\My Documents\MyWeb\here.html to
C:\My Documents\JavaScriptGoodies\thanksalot.html
href="../JavaScriptGoodies/thanksalot.html"
../ takes it back one folder level (My Documents)
JavaScriptGoodies/thanksalot.html path from My Documents
To go from C:\My Documents\MyWeb\here.html to
C:\New Folder\New Page.html
href="../../New%20Folder/New%20Page.html"
../../ takes it back 2 folder levels (My Documents, C

New%20Folder/New%20Page.html path from C:
I am not sure of the path to the page you were at when you started so I gave you the full path. I bet it would work if you just simply put this in:
onDblClick="location.href='../JavaScriptGoodies/thanksalot.html'";>
add another ../ for each folder level you have to go back to get to the intended path.
Brian