Do you only have one pNIC to use on this server? If you have more than the one port to use, then try setting up a seperate vSwitch for VM only traffic. Such as the way shown in the attached screen shot (from my ESXi 4.1 host)...
I would also set the MAC Address CHanges and Forged Transmits to "reject"...
I would also try building a new VM from scratch to see if it can get an IP when the other (original) one is powered on... If it can, then you did something wrong in the sysprep process.
BTW, I would not advise using two VM Network port groups in the same vSwitch... I would also not use the same vSwitch that you use for the Management Network for VM Network traffic. Even though ESX/ESXi makes a VM Network port group within the same vSwitch, I wouldn't use it. Better to make another vSwitch for VM communication/traffic and keep it isolated from the vSwitch that's for the Management Network. You do have two Gb NIC's onboard with that server (on the motherboard). You can also install another NIC (or two if you're not using both PCI slots) that's a dual port (supported, or on the HCL for ESXi 4.1).
I would also not use 100Mb networking for ESX/ESXi... If it's set to 100Mb due to the switch you're connecting to, get a Gb switch to take it's place. You can get an unmanaged Gb switch pretty damned cheap these days. Of course, I prefer to use managed switches when connecting up ESX/ESXi host servers, even in my home lab.
If you can get a copy/license for vCenter Server, use that to administrate the host server. This will give you access to using Templates to deploy new VM's. This is a far, far, far better way than using the old sysprep routine. I've used it with great success for some time now...
Network Administrator
VMware VCP4
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