In your blood folder open the ''dosboxBlood.conf'' and edit the type of machine that Dosbox emulates to ''machine=vesa_nolfb'' without the quotes.
Resolutions above 800x600 vill no longer be flickering.

cool, it also seems to fix an issue some folks have been having with the HUD render when changing in-game resolution with the +/- keys.

It does seem to bring up issues with the way BMOUSE works however. I keep crashing back to desktop with vesa_nolfb. I am on Windows 7 64-bit.

Strange, Blood has never crashed on me even with this fix.
But then again i'm using Windows 7 32-bit, It does seems to be common for some of these games to have various issues when using the 64-bit version.

I re-downloaded BMOUSE 0.6 to be sure I was actually running the latest version. I've only run it once since then but it hasn't crashed yet, so I suppose I may have still been running 0.5

Okay, also what version of Dosbox are you using?
Blood from GOG comes with version 0.73 and the latest is version 0.74.
It would be a very good idea to update to 0.74 since Blood runs much better.
Just download and install Dosbox, Then copy the dosbox exe file to the dosbox folder in blood, you can just overwrite the old exe.

I just double checked DOSBox, I'm running 0.74. I must have been running the old bmouse.

Super, I hope the game is gonna stop crashing on you.