Vista installation problems with ATI HD2600-series grafic board

I have tried to intall Windows Vista on systems using HD2600Pro and HD2600XT
grafic boards but it is impossible. The installation starts and I get to the
point where I can select "Install now". The time it takes to get there is
around 20 minutes. When selecting "Install now" I interupts the installation
after one hour because I still waits for the system to start the installation.

If I installes Windows XP on these systems the installation runs without any
trouble what so ever.
The first system contains Gigabyte GA-M56S-S3 motherboard, 4 times 1GB
Corsair PC6400 RAM, AMD X2 5600+ , Xilence 650W PSU and Sapphire HD2600XT
grafic board, Samsung Spinpoint 500GB 16MB SATA and Seagate 250GB 16MB SATA
drives.

The second system contains MSI AGM-3FH motherboard, 4 times 1GB Corsair
PC4300 RAM, AMD X2 4200+ , 350W PSU and GeCube HD2600Pro grafic board Samsung
Spinpoint 500GB 16MB SATA. and WD 250GB 8MB SATA drive.

Both system has been tested with just one memory module and with an 80GB IDE
hard drive too. The SATA drives has then been disconneted. The grafic boards
has been swopped between the systems without any change.

If a grafic board ATI X1650Pro is installed in the systems Windows Vista
will install successfully! If the X1650Pro is replaced with HD2600Pro or
HD2600XT after Vista installation the Vista installation crashes when the
driver ATI Catalyst 8.1 is installed (7.9 version contains a bug). The Vista
system becomes very unstable with HD2600 series grafic board installed and
can not be used.

If a nVida 8800GT is installed in the system the Vista system runs without
any problems what so ever.

Why does Vista have these problems with HD2600 series of grafic boards?

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Marathonkillen still runs