As Simon explained, as long as you are using PHP on Dreamhost you will have to jump through some significant hoops to upload files of that size.
Another alternative that would work well in your situation is to use an upload script or file manager written in Perl. Such a script does not have this filesize limitation, and there are many such scripts around the web that work well on Dreamhost.
Two that I have used and can recommend are:
1) ffileman - very easy to install, simple interface, but very functional
2) FileMan - Been around forever, very powerful, marginally more difficult to install, but very popular.
Both of these are "free" and, once installed in your Dreamhost web space, give you password protected access via a browser (so you can use it at work) to much of the same functionality as you find in DH's webftp, but since they are written in Perl instead of PHP, you will not have the filesize limitation.