Paco, I just went through a similar exercise with a different RealTek NIC. I don't know if there is any "official cookbook" or perhaps a simpler approach, but here's a sample procedure.
From your ESXi console, scp these two files out to your CentOS box (if you've got a dual-boot setup with ESXi and CentOS, you'll need a 3rd Linux machine or else will need to enable some kind of SSHD on your XP box):
scp /etc/vmware/simple.map myname@mycentosbox:/tmp
scp /etc/vmware/pci.ids myname@mycentosbox:/tmp
Go to your CentOS box.
To modify /tmp/pci.ids, look for the RealTek section (10ec) and simply add a line for the 2a01 device, e.g.
10dc Realtek Semiconductor Co, Ltd.
0139 Zonet Zen3200
2a01 My Funky RealTek NIC
To modify /tmp/simple.map add a line anywhere that looks something like:
10ec:2a01 0000:0000 network r2a01.o
The hard part is that module r2a01.o, which as Dave writes you'll need to compile yourself. If you're lucky, someone may have already posted a compiled driver file, but if you can't locate one via Google you can look for the source code at RealTek's website: http://www.realtek.com.tw/downloads/dow ... l=3&Conn=2
You should compile the code on a 64-bit version of Linux -- as always, YMMV.
You can try scp'ing the newly-compiled r2a01.o file into ESX and trying the vmkload_mod Dave mentions, or you can go for the gusto and just try a deployment.
To bundle everything up for deployment, from your CentOS host you'd do something like:
# Create skeleton dir tree
mkdir -p /etc/vmware /usr/lib/vmware/vmkmod
# Next copy in the files you either modified or compiled
cp /tmp/simple.map /etc/vmware
cp /tmp/pci.ids /etc/vmware
cp /src/realtek/r2a01.o /usr/lib/vmware/vmkmod
# Tar things up
tar cvf /tmp/oem.tar /etc/vmware /usr/lib/vmware/vmkmod
mv /tmp/oem.tar.gz /tmp/oem.tgz
# Mount the ESX partition that contains the oem.tgz file and copy in your new one.
# On my setup, the commands were:
mount /dev/sdb5 /mnt
cp /tmp/oem.tgz /mnt
NOTE: I'm assuming that the existing ESX oem.tgz was empty (which it usually is, unless you had modified it yourself), otherwise you'd have to modify the above procedure to save the existing oem.tgz data and repackage it along with your new stuff.
Boot up ESX and see if the driver has loaded -- if it doesn't, you'll simply see warnings in /var/log/messages, it won't actually stop the system from booting. If you're lucky, though, the new NIC will already be working.