This is weird. I'm am not having any issues at all. Not with my 5830, nor the three 4850. That's four cards across three systems, Win7 Home premium, WinXP Pro and Win7 Ultimate (all are x64).
BOINC Manager v6.10.58 (All 3 systems)
Milkyway App app 0.82
HD 4850s - ATI Catalyst 10.10 (w/o OpenCL)
HD 5830 - AMD Catalyst 11.5 (w/ OpenCL)
Edit: Just to be clear, the ATI CAtalyst 10.10 driver comes in two versions for each OS platform.
Example:
Without OpenCL: 10-10_vista64_win7_64_dd_ccc_enu.exe
With OpenCL: 10-10_vista64_win7_64_dd_ccc_ocl.exe