More information about your machine would indeed be very helpful (as much as possible...).

As far as I know, all the drivers used when booting windows are still provided only by apple. Maybe there's some way to update your drivers (don't forget to backup your files just in case).

PS: Could you also provide the temperatures during gaming (aux, GPU, CPU should be enough)?

Hi ThermioN, thanks for answering! To save space here I've posted my full dxdiag report to my Dropbox (50KB, should open in browser).

Short version: Quad 2.93GHz “Nehalem” Xeons, ATI Radeon HD 4870, 6GB RAM, of which 2GB visible to WinXP 32-bit (SP3, fully patched). Being a cross-platform dev, I can answer this part definitively. There's no magic in Boot Camp, Windows just boots on the metal as in any multi-boot setup. Boot Camp just gives a nice UI and a set of drivers to get you going, but after that you can install any drivers you please. (The first Intel Macs needed an EFI update to enable booting Windows, but Apple delivered that via firmware update, not Boot Camp.)

When I first saw the gun XP meter bug, I was using Catalyst 9.10. I've just installed Catalyst 10.9 and I'm still seeing it. My old iMac that doesn't show the gun XP meter bug is still on Catalyst 7.11. Before anyone asks, when changing Catalyst drivers I always take the clean route as per tweakguides.com. I don't overclock and the only tool I have for reading temps is the Catalyst control panel.
When idle:
Temp 66C Activity 0% Fan speed 9%
After alt-tabbing out of an active BloodRayne2 game:
Temp 88C Activity 99% Fan speed 22%.

I don't think CPU temp is an issue as I've never heard the fans spin up.

Other things I've tried:
1280x1024 with all four options in the starter app lowered: no dice.
800x600 with all four options in the starter app lowered: no dice.

This leads me to think it's an ATI Catalyst update issue, but if so, why is no-one seeing it?

Edits: fixing the quote tags.

So, to get this straight...
You've already tried different versions of the CCC on your mac?
How about other drivers on your system? Are they all up-to-date?

As you may know, updating your drivers may cause other things to fail. So I would recommend backing up your files (an Image of your windows partition would be the best solution).

Your temps are OK. This should not be the cause of your problems.

I'm not that familiar with the CCC, but maybe you're forcing some features like FSAA, ambient occlusion or transparency antialiasing (not sure if these features are available for ATI/AMD GPUs...).

I also "googled" BloodRayne 2 community-made patches, but I only found tons of nude or FSAA patches :(

Thanks, ThermioN, for your help so far. I've tried Catalyst 9.10 and 10.9 only. All other drivers are the baseline from Apple Bootcamp, but I'd be amazed if they were to blame as they're just sound, WiFi, Bluetooth etc. Yes I know. I image my windows partition to an external HDD using Norton Ghost 10. (BTW I'm open to better, more modern solutions but have yet to find one.) Nope, everything is set to application-controlled. I'm going on vacation for a week, but when I get back I'll have a play with the settings in CCC and see what differences they make.

PS Any thoughts about "Bug 2: jump to infinity"? That's actually rather more annoying in gameplay than the purely cosmetic bug with the gun XP meter. It's kinda random, but happens most often when I double-tap the space bar when a time-slowing power is active.