1.
First install GreaseMonkey from here.

2.
Copy the contents of the script into a text file with a plain text editor like Notepad and name the file "increase_font_nokia.user.js".

3.
Send an email to your NIT with the script attached

4.
Finally open and install the attachment on your NIT (can't remember if the browser must be opened at that time).

More useful scripts can be found here. Or specific for the N810 here.

Thanks! Having just tinkered with the maemo Greasemonkey UI, I see that if you choose New User Script in the menu, it'll create a user.js file and open up Notebook automatically for you. I had no idea!

Thanks again!

Also, for those who wish to increase font on all or specific urls, more info in this thread.