Hard Drive Will This Work

Hi There
I am in the process of looking in to renewing the hard drive on my laptop.
It is a EI System 4430 running windows XP SP1. The hard drive in question is a Toshiba MK4025GAS 40GB UDMA Mode 5 ULTRA ATA/100 Firmware Version KA100A.. The Motherboard is a MID2020 Version A1 with a Chipset of SIS Version S2054S the Motherboard real clock is 100MHz Bios INSYDE Technology.
My problem is that I have found a H Drive on the web made by Toshiba with the same model No MK4025GAS 40GB the only difference is that the new one is ATA133 and mine is ATA100. I tend to think this will work in my laptop albeit at the slower transfer speed of ATA100. Can anyone tell me if I am correct in my assumption or will I have to find a HD that works at ATA100. I have run a free program to collect some of this Info and it says Supported ATA Standard is ATA1, ATA2, ATA3, ATA4, ATA5 and ATA6. I have tried EI Systems helpline but they want to charge me