permissions issue during installation of Prestashop 1.2.5 on commercial hosting server

[dimotar]

Dear friends, I encounter serious problem during Prestashop installation.
I use commercial hosting provider AGAVA- one of best on russian market. I have FTP, SSH, cPanel, MySQL, PHP5, all bels and whistles except for 777 write permissions for folders. Their default value is 755 for folders and 644 for files.
Last time I tried to give 777 permissions to folder the site was immediately and completely blocked by their security policy.
This time I've managed to change to 775 for folders. Take a look at screenshots to see what happened next.
All phases untul 4th are flawless. When I put admin data and press NEXT progress bar shows up for short time and than nothing. Absolutely nothing- no errors reported, no blockings, nothing, I could press NEXT many times more- same thing.
When I open /store in sepatate browser window I see shop showing up, but I can not log in neither at front office nor at back oone (sure, after renaming /admin and removing /install). Interestingly, settings.inc.php gets written with correct data and obtains actual date/time. So install can write in /config folder with 775 permissions, wha'ts up with others?
So the question is simple- what to do? These guys from [email protected] will not allow me 777 for folders even for a second. I've paid one-year subscribtion and I prefer to benefit from this investment, since there is no money-back from AGAVA.
I can do full install on local WAMP server without any problem. Could I later somehow combine remote+local install?
Thanks in advance for helping me,
a bientot.
Vieux Toulousain Dimitri TARASSOV.