X6 Installation: Error Writing To File: C:\Program Files\Corel\.......

I have Just downloaded X6 Spanish trial to upgrade from old x4 install. I'm running XP SP3, Intel Dual Core 1,6 GHz, 4 GB RAM, more than enough HD space and compatible video card. I've been trying install it for the last 20 hours or so, but to no avail. I keep getting the following screen at 35% progress of the installation:

 I have tried ALL the recipes I could find mentioned here: Ran CCleaner, ran ChkDsk, ran memory check, uninstalled antivirus, ran MSCONFIG and restarted both in selective mode and in diagnostics mode. Created a new account with admin rights. Ran a full virus scan, reset IE8 to default settings and made it default browser. Uninstalled all my Adobe applications. Probably I am missing something. I did lots of stuff.

To make things worse I also uninstalled X4, and I really don't have a clue about where the installation disk might be. So now I got nothing! I need help, please!!!

Have you seen this particular error before? is there a solution?

Thanks