Installing and upgrading help

I hope I've chosen the correct forum for this issue.  If not, my apologies.  I'll happily move elsewhere.

We've had two installations of Moodle running happily using v1.4.3  In order to try out the new database module we needed to be running a current v1.5 Moodle.

I downloaded the zip file of the current dev release and installed these on the development machine and all worked just nicely.  I have access to this machine and was able to install the files on that machine.

The main machine is remote from me and I have only FTP access.

I transferred the new files by FTP apparently successfully.

Upon completion I went to the front page of Moodle and it was immediately apparent that all was not well.

The colour theme is now missing.  The updating of the files began but soon failed with the following error:

PHP Warning: main(D:\InetPub\iice\moodle/lib/filelib.php): failed to open stream: No such file or directory in D:\InetPub\iice\moodle\mod\forum\lib.php on line 3

I tried going direct to the login page.  Again this appeared without a theme but all the expected login text was present.

I provided my user id and password and clicked the login button to receive the following error:

PHP Fatal error: Call to undefined function: sesskey() in D:\InetPub\iice\moodle\login\index.php on line 102

Can anyone offer a way out of my problem?  The files appear to have begun to be converted and I'm uncertain what action to take.

Advice very gratefully received.

Andrew