modem connection speed

I recently submitted this question but could not find it posted.
I have a new PC with Windows XP and a .V90 PCTel Platinum modem. I have to set my max connection speed at 9600 bps or I will not be able to connect. My IPS’s computers’ protocol errors and timeouts prevent connecting. My ISP is not willing to help as they are not up to date on WinXP. I’ve tried adding strings from the modem website, changing all the parameters possible, but to no avail. Compaq had me connect to an 800 number ISP with no problem. I know that this modem is software driven and has been known to cause this type of problem. Is there anything I can do to try to connect at a higher or max speed. Thanks.