Nokia n95 as usb modem

i have a nokia n95 and i use it as a usb modem for my p.c to access the web. my network provider is t-mobile. when installing the device it is registered on my system as a nokia n95 'gsm' modem yet the nokia n95 is said to have hsdpa technology allowing faster access as long as i am in a 3g area.could you tell me why this is? or maybe where i may have misunderstood part of the initial interpretation of the nokia n95, making me think that i should be getting more than i actually can from the phone?....also, as a usb modem, when it is connected the maximum speed i can recieve is 921.6 k/bs when i have altered my settings on my p.c (operating system windows xp sp2)...how can i recieve faster connection speeds, if possible? t-mobile reckon they can offer speeds TWICE as fast as im getting (upto 1.8 m/bs) but i dont see how this is possible when a usb modem can only be set to the speed that i am recieving now when maxed out. thanks for at least listening to my problem whether you can help me or not and thanks in advance for any advice you can offer me. micky cleary, durham city, england