To elaborate on what has been said....
I believe what you have done so far is, essentially, use your BB as an analog modem. I expect that the airtime for that would be charged against your voice minutes. And it would be really slow.
Your better options are:
1) Pay your carrier a monthly fee for tethering and then use your BB as a "digital" modem. That would be a lot faster and go against your data plan, instead of voice minutes. Assuming you have an unlimited data plan, the montly fee for tethering (usually around USD$15 per month) would be your only extra expense.
2) Use Tetherberry. It has a one-time up front cost (I think USD$60 now). It does not put your BB in Modem Mode. Instead, it makes your BB function as a router and DHCP server. The Tetherberry software that you install on your PC installs itself as a USB Ethernet adapter driver. From the carrier's point of view, it just looks like your BB is sending and receiving a lot of data over the Internet, which is covered by your existing data plan.
Be aware that use of Tetherberry may not be allowed under your carrier's Terms of Service. As an example, Verizon's Terms of Service for the Blackberry Unlimited Data Plan specifically forbid use of the BB as a device for tethering to a computer (unless you pay them for tethering, of course). However, numerous people have reported calling Verizon Customer Service and inquiring about the use of Tetherberry and being told that Verizon doesn't care.
I have personally used Tetherberry all day, every day (8 hours per day, 5 days per week), for several months, with my laptop, and it has worked nearly perfectly and Verizon has never said anything to me or charged me any extra.
Verizon 8130 (on the bench, now
Verizon 9530 (replaced by VZW 4 times, then with a 9550)