I've installed the
gdk_pixbuf for lib32 now.
Solution for Ubuntu 5.10 AMD64:
1) Download libgdk-pixbuf2_0.22.0-8ubuntu0.1_i386.deb:
http://packages.ubuntu.com/breezy/libs/libgdk-pixbuf22) Unpack package: ar -x libgdk-pixbuf2_0.22.0-8ubuntu0.1_i386.deb
3) Unpack data: tar -zxf data.tar.gz
4) Copy files: sudo cp -rp usr/lib/* /usr/lib32 (There is no forward slash at the beginning of the first path.)
5) Fix symbolic links: sudo ln -s /usr/lib32/libgdk_pixbuf.so.2.0.0 /usr/lib32/libgdk_pixbuf.so.2
6) Update ldd cache: sudo {libconfig,ldconfig} (Optional!)
I've installed the FreePascal 2.0.0 x64_86 on my Ubuntu 5.10 AMD64. The configuration file, '/etc/fpc.cfg', was generated using the method written in the Wiki. Replaced all static version information (2.0.0) with $fcpversion.

Checked out the lastest SVN revision, but no luck today, the error is also there, I've reported some time ago here in this thread...
Ok, because of this error compiling FreePascal SVN using FPC 2.0.0 x64_86, I'm using the 2.0.0 build so far.
Then I downloaded the Lazarus RPM, unpacked it and checked the lazarus binary with ldd. All clear, ldd found the new installed gdk_pixbuf, woohoo.

Lazarus (off. build) starts up, and notices me that no compiler was found. Ok, I could set all settings so I can use Lazarus, but I want a complete x64 env. So, I compiled Lazarus SVN with the current official FPC release 2.0.0 x64_86, no errors so far.
Starting up Lazarus (my build) givs me an error:
./lazarus
TApplication.IconChanged - TODO: convert this message...no implementation in gtk or win32
[FORMS.PP] ExceptionOccurred
Sender=EReadError
Exception=Error reading SplashForm.HorzScrollBar.Page: Access violation
Stack trace:
$00000000004A3CEA
$00000000004A3095
$0000000000497DDD
$00000000004A4B4A
$0000000000575E62 INITCOMPONENT, line 2098 of lresources.pp
$0000000000575C5F INITLAZRESOURCECOMPONENT, line 2117 of lresources.pp
$0000000000429BED INITRESOURCECOMPONENT, line 1376 of forms.pp
$000000000042FE4A TCUSTOMFORM__CREATE, line 1257 of ./include/customform.inc
$0000000000443FC3 TSPLASHFORM__CREATE, line 72 of splash.pp
$000000000040F638 main, line 70 of lazarus.pp
TApplication.HandleException Error reading SplashForm.HorzScrollBar.Page: Access violation
Stack trace:
$00000000004A3CEA
$00000000004A3095
$0000000000497DDD
$00000000004A4B4A
$0000000000575E62 INITCOMPONENT, line 2098 of lresources.pp
$0000000000575C5F INITLAZRESOURCECOMPONENT, line 2117 of lresources.pp
$0000000000429BED INITRESOURCECOMPONENT, line 1376 of forms.pp
$000000000042FE4A TCUSTOMFORM__CREATE, line 1257 of ./include/customform.inc
$0000000000443FC3 TSPLASHFORM__CREATE, line 72 of splash.pp
$000000000040F638 main, line 70 of lazarus.pp
Runtime error 217 at $000000000041B1C5
$000000000041B1C5
$000000000041B6D3
$000000000044405A TSPLASHFORM__CREATE, line 71 of splash.pp
$000000000040F638 main, line 70 of lazarus.pp
Error log is from the situation if I press Ok. In both situations nothing happens, Lazarus don't start correctly.
Nice screeny here:

(http://img105.imageshack.us/img105/1691/accessviolation0qg.png)
Perhaps it is not good to mix up the versions, I think all the problems go away when the broken FPC will be fixed. I looked into the files, but, no idea so far.
Any suggestion?
Thanks,
RGB