Grub can not find this kernel
This could be for several reasions.
The name of the kernel is wrong (since this is a xen kernel this would not supprise me). Try editing the line in the grub boot loader and remove the "xen" from the end of it.
Grub is looking in the wrong place on the file system for the kernel.
Again there is a good chance that this was caused by the V2V, possibly changing the partition numbers.
To fix this one try running the following at the grub prompt:
grub > find /vmlinuz. This should display the something like the following.
Note that if it is different use what grub shows, it should be in the format (hd,X,Y)
Next to get the full name of the kernel type
grub > null (hd0,0) /vmli and press TAB
This should output something like the following:
Possible files are: vmlinuz vmlinuz-2.6.18-194.17.4.el5, vmlinuz-2.6.18-194.17.4.el5xen
Let's say for this segment that the kernel is called (again use the grub output from the prevous line to guide you):
Now that you know the full name try typing the following:
grub > root (hd0,0)
grub > kernel = /vmlinuz-2.6.18-194.17.4.el5 root=/dev/VolGroup00/LogVol00
grub > boot
This should boot the system (hopefully as long as nothing else is wrong).
Once you are up and running you will need to reconfigure grub.
There is plenty of data on google showing how to do this.