There is a way to do it of course but it's so much easier through official package repositories, this way it's safer because with Inkscape also all the libraries that Inkscape may depend upon will be installed with it, in case you already don't have them.
I'd recommend fixing the internet connection, it's usefull for so many other things than just installing new software
Have you found some tutorials about setting up the wireless on ubuntu? I know it can be tricky on some laptops, and especially if there are many networks active in your area sometimes they interfere. Ubuntu forums and chat room are great places to get help, don't forget to search first!
And no you shouldn't stay with Vista

I'm shameless
If you must try the "dry" download check out Inkscape download page and look for Autopackage area.