Welcome to the wonderful world of ACPI.
Don't worry. I have 6 devices sharing IRQ11 in my Win2K, namely:
1. ATi RAGE FURY 16MB (AGP VGA)
2. Adaptec AHA-2940U2W-Ultra2 SCSI (PCI)
3. ALi USB Host Controller (onboard)
4. OPTi USB Host Controller (PCI)
5. Creative SB Live! (PCI)
6. Leadtek TV2000 Video Capture (PCI)
Absolutely no problems here, except some occasional jerky movement when watching DVDs and other videos when my SCSI disks are accessed (Adaptec's SCSI cards are quite bus-hungry), but practically solved after a SCSI BIOS update

Note: when I had a SUPRA modem (PCI), before moving to ADSL, it ALSO used IRQ11, so that totalled 7 devices. And everything worked ok.