I've visited Taxila twice in May 2004; the site can easily be reached from the Grand Trunk Road, which connects Islamabad and Peshawar.

There are several subsites at Taxila, such as Bhir Mound (the oldest part), Sirkap and Sirsukh (two later cities), a giant stupa, a Greek-style temple (called Jandial) and several Buddhist monasteries. A bicycle or a rented taxi can be useful, because the distances between these parts of Taxila are pretty large. At all these sites, it is easy to hire an English-speaking guide, but I was not always impressed by their quality.

The museum is excellent.

More info at http://www.livius.org/ta-td/taxila/taxila.htm