Problems with executing .php in top level folder since platform upgrade

[#1]

After the problems a couple of weeks ago, I found that my website (http://bish.co.uk) no longer worked.
After some fiddling with permissions using CHMOD, I  managed to get some .php to execute on my website.
I found that http://bish.co.uk/forum/index.php still works but http://bish.co.uk/index.php (my main website) had the "premature end of script header" problem.
I found that by moving the index.php from the top level to a sub folder fixed the problem. Now I have my main site at http://bish.co.uk/joomla/index.php and it works.
Unfortunately any .php file that I put into the top level folder refuses to execute. I can't even run http://bish.co.uk/test.php which only contains the following text. <?php phpinfo(); ?>
If this is a change to prevent attacks of the sort that brought down the old sites then I'm happy, but I'd like to redirect requests for http://bish.co.uk or http://bish.co.uk/index.php to the new joomla subfolder.
I'd also like to remove my username from the URLs which are shown to a user.
If anybody can advise on this I;d be really grateful. I logged calls a couple of weeks ago about this and despite updating my call with regular comments and requests for updates, I haven't heard anything from PlusNet support.
Does anybody know if I move to the PAYH service whether I can get better support if I'm prepared to pay for it?

[#2]

If you run

#!/bin/bash
echo "Content-type: text/plain"
echo
ls -l -d ../

anything.cgi from a subfolder of your root, does it tell you that your root has drwx--x--T (1710) permissions and is owned by username and group cgiusers?
Gabe

[#3]

Thanks for the prompt advice Gabe.
I've tried to use PUTTY (both SSH and Telnet) to connect to my CGI space but I get "connection refused" errors.
Are there any more comprehensive instructions for using PUTTY than those found at this link?
http://www.plus.net/support/webspace/cgi_php/cgi_guide.shtml#telnet

[#4]

We are sadly sshless - see faq. If you ftp the script to your subfolder and set its permissions to 700, you can call it in your browser. It will then show that, for some reason, your root folder is 1737. This is wrong.
If you raise a ticket and ask for it to be set to 1710, that'll fix it. Or perhaps some passing plusnet wizard will notice this thread and fix it first.
Gabe

[#5]

Thanks Gabe. I followed your instructions and put the CGI file in a sub folder.
When I ran it I got this result......
drwx-wxrwt 5 {username} cgiusers 4096 Mar 25 09:08 ../
I'll raise a ticket and ask for the permissions to be changed.
You've been a great help, thanks.

[#6]

I followed your advice, logged a call with PlusNet and they fixed my permissions.
All is now well with my site ! The sites at http://bish.co.uk and http://bish.co.uk/forum now work again.
Thanks very much for your help Gabe.