You did the Xen kernel compile,
please set the dom0.

１．Check the your analog-PCI-Card(ex.X100P).

[root@asterisk ~]# lspci

It is my case.

00:00.0 Host bridge: Intel Corporation Mobile 945GM/PM/GMS/940GML and 945GT Express Memory Controller Hub (rev 03)

00:02.0 VGA compatible controller: Intel Corporation Mobile 945GM/GMS/940GML Express Integrated Graphics Controller (rev 03)

00:02.1 Display controller: Intel Corporation Mobile 945GM/GMS/940GML Express Integrated Graphics Controller (rev 03)

00:1b.0 Audio device: Intel Corporation 82801G (ICH7 Family) High Definition Audio Controller (rev 01)

00:1c.0 PCI bridge: Intel Corporation 82801G (ICH7 Family) PCI Express Port 1 (rev 01)

00:1c.4 PCI bridge: Intel Corporation 82801GR/GH/GHM (ICH7 Family) PCI Express Port 5 (rev 01)

00:1c.5 PCI bridge: Intel Corporation 82801GR/GH/GHM (ICH7 Family) PCI Express Port 6 (rev 01)

00:1d.0 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #1 (rev 01)

00:1d.1 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #2 (rev 01)

00:1d.2 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #3 (rev 01)

00:1d.3 USB Controller: Intel Corporation 82801G (ICH7 Family) USB UHCI #4 (rev 01)

00:1d.7 USB Controller: Intel Corporation 82801G (ICH7 Family) USB2 EHCI Controller (rev 01)

00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev e1)

00:1f.0 ISA bridge: Intel Corporation 82801GB/GR (ICH7 Family) LPC Interface Bridge (rev 01)

00:1f.1 IDE interface: Intel Corporation 82801G (ICH7 Family) IDE Controller (rev 01)

00:1f.2 RAID bus controller: Intel Corporation 82801GR/GH (ICH7 Family) Serial ATA Storage Controller RAID (rev 01)

00:1f.3 SMBus: Intel Corporation 82801G (ICH7 Family) SMBus Controller (rev 01)

02:00.0 Ethernet controller: Intel Corporation 82573L Gigabit Ethernet Controller

03:00.0 Ethernet controller: Intel Corporation 82573L Gigabit Ethernet Controller

04:00.0 Communication controller: Tiger Jet Network Inc. Tiger3XX Modem/ISDN interface

04:04.0 FireWire (IEEE 1394): VIA Technologies, Inc. IEEE 1394 Host Controller (rev 80)

「04:00.0 Communication controller: Tiger Jet Network Inc. Tiger3XX Modem/ISDN interface」　is my analog-card(X100P).

Please check the first number.
My casa is [04:00.0].

２．Add next comment.

[root@asterisk ~]# vi /etc/rc.d/rc.local

# add the comment

modprobe pciback

sleep 2

SLOT=0000:04:00.0

# Add a new slot to the PCI Backend's list

echo -n $SLOT > /sys/bus/pci/drivers/pciback/new_slot

# Now that the backend is watching for the slot, bind to it

echo -n $SLOT > /sys/bus/pci/drivers/pciback/bind

３．Set the boot loader.

[root@asterisk ~]# vi /boot/grub/menu.lst

# Add the next.

title CentOS (2.6.16.33-xen)

root (hd0,0)

kernel /xen-3.0.4-1.gz dom0_mem=256M

module /vmlinuz-2.6.16.33-xen ro root=/dev/sda3 ro console=tty0 pciback.hide=(04:00.0)

module /initrd-2.6.16.33-xen.img

４．Reboot the your system!

And you start the Domain0 and DomainU!

When your domainU is run, please chech the next command.

[root@asterisk ~]# lspci

My case, I get the next message from domainU.

04:00.0 Communication controller: Tiger Jet Network Inc. Tiger3XX Modem/ISDN interface

If you can meet the message, your domainU use the Analog-PCI-Card(ex.X100P,TDM400P).