pci-e ati graphics card conflicts with pci ati graphics card?

(this is a double post to general hardware - just trying to reach out to as many people as possible!)

hi everyone,

i'm trying to get two graphics cards into my desktop, but am having trouble getting both cards to be recognized at the same time. has anyone had this problem, and found a solution? any ideas much appreciated! here's the situation:

relevant aspects of my computer:

• dell xps410/dimension 9200
• bios version 2.5.3
• chipset version 8.0.0.1009, A17
• pci-e sapphire radeon hd 3870, catalyst drivers 9.4
• pci powercolor radeon hd 2400 pro, catalyst drivers 9.4
• i have 2 SATA hdd's installed, 1 SATA burner, and 1 modem.
• running windows xp SP2

the problem that i'm having is that i can't seem to run both graphics cards at the same time. both cards are correctly installed. i know this because i can use each one separately - just not both at the same time. to use one card or the other, i change which card is "primary" in the bios.

if i boot up with the pci-e graphics card as primary, then windows sees that card and uses it fine. device manager, however, also shows the pci card but with a yellow exclamation on top of the icon. when i right click that, it tells me that the "device could not start (code 10)" (or something to that effect). the event manager occassionally also tells me that the computer is "Unable to map required address ranges for graphics card" - and this error is "event ID 2" and the source is "ati2tmag."

if i boot up with the pci graphics card as primary, then windows sees that card and uses it fine. device manager, however, does not even show the pci-e card. instead, it giveds me a yellow exclamation on top of the pci-e root port. when i right click that, i find that this device could not allocate sufficient resources, suggesting an IRQ or memory addressing conflict. that said, pulling out other devices doesn't resolve this problem. neither does changing the pci slot that the card is seated in.

does anyone have any thoughts as to why this is going on? my suspicion is that my particular dell motherboard/bios combination for whatever reason cannot support having a pci-e graphics card and a pci graphics card a the same time. everything at a higher level seems to be working correctly - it's just that there's a resource conflict now that is preventing both cards from loading simultaneously. if this is the case, is there some way to manually assign resources to the two cards?

thanks in advance.

jonathan