Stop error when installing modem

I hope I am in the right place and someone can help.

I tried to install a Zoom USB V.92 model 3090 modem on a new computer,
running XP pro sp1. The installation went alright, got to the drivers not
being signed warning, continued, and managed to install. I found that I
wasn't getting enough power to the modem to light it up, so uninstalled it
and tried to install the Zoom V.92 serial modem, model 3048. This time when
I tried to continue past the drivers warning, the system crashed and I got a
Stop error screen. The error message: IRQL_NOT_LESS_OR_EQUAL, and under
technical error: Stop 0x0000000a (0x0000ffdf, 0x00000002, 0x00000001,
0x806bd90e). I have also got Stop 0x0000000a (0x0000f87c, 0x00000002,
0x00000001, 0x806bd90e).

I then tried another brand modem, and can't get past the drivers not being
signed.

I have searched the MS database without finding reference to these errors,
and it is my understanding that after warning that the drivers were not
signed, XP should allow the installation. Does anybody have any answers or
suggestions for me? How do I get back to the place where XP will allow me to
install drivers that aren't signed? How do I make sure I have uninstalled
the modem drivers? Can anyone recommend a modem that supports V.92 and V.44,
and comes with XP signed drivers. Thanks.

DavidF