I had a similar problem straight after becoming upgraded to broadband.
My connection was very random, more off than on, and it finally went off all
together.
I was given the run around by 'Technical Support' about drivers, splitters,
modems etc.
My 530 modem was giving me an error message 'Modemline Down' was would not
synchronise.
It took BT about 9 days to send out a phone engineer to test the line on
site and he couldn't find a line fault, but passed it onto an adsl
specialist engineer who took several more days to come out.
Fortunately the adsl specialist knew what he was doing and detected that my
line was good for PSTN regular phone use but not for ADSL, that's why it
kept going off.
Luckily there was a new underground cable between me and the exchange and
the adsl engineer transferred me onto it. Everything has been fine since, no
dropped connections at all.
The unfortunate thing is that BT only send out the specialist as a last
resort, so you will probably be messed around for a week or 10 days 'till
they send someone who knows what they are doing.
By the way, if you ask for the adsl specialist to come out before the PSTN
man has been and decided he can't fix it, your ISP or BT will probably
threaten you with a bill for £150 if they send the specialist and he find
the fault is with your PC.
This is a good site for broadband info and help.
--
http://www.adslguide.org.uk/