[pie's husband here]
At risk of being told off by some "programmer's wife" for not knowing what I'm talking about, here is my advice and hope it helps...
First and foremost, you have to find out what kind of DVD player it is then go to that company's own site for drivers. HP may have 'recovery' drivers, but they won't keep up on updates or what-not. If you are lucky, your hardware profile will have the name and model number of your DVD player. (To find this, go into your control panel, double click the system icon, under the 'Hardware' tab, the device manager button, then in the new window, click on the '+' sign next to "DVD/CD-ROM Drives". What it says there is your drive name and model number. In my case, it is Lite-on LTD-163D. I'd just go to www.liteon.com and look in support or drivers for the model.)
That said, you may not have to reinstall your drivers... With luck, your DVD player hasn't locked itself. All DVD players (some exception, but not many, especially any shipped in a pre-configured machine like HP), have a pre-set amount of times you can reset your region. Follow the above instructions to get into your DVD properties (going into control panel). Once you click on the '+' next to DVD/CD-ROM Drives, right click, left click on properties, click on the "DVD REGION" tab, scroll down until you get to UK and click ok. This will force your DVD back to Region 2. If you get to this page and where it says "Changes remaining:" and it says 0, you are out of luck. There is NOTHING you can do to change it back to Region 2, it is now stuck at whatever region it is set at forever. However, there is a work around... Get yourself a copy of PowerDVD (cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=3616751771&category=182). This is a software package that will play your DVDs regardless of region code.
Like I said, I hope this works, and I hope I made sense...