There are few direct flights to Afghanistan from outside the immediate region. The most popular route from Europe or North America is to fly to Dubai, from where there are plenty of connections to Kabul. Coming from the east, the most convenient hubs to catch flights from are Delhi and Islamabad. When entering the country by air, formalities are fairly simple, but be prepared for long queues. Baggage reclaim can sometimes be something of a scrum, but at least the carousel normally has electricity these days. Customs checks on arrival are fairly cursory. Currently only Kabul International Airport (tel: 020 2300 016) receives commercial flights into Afghanistan. There is an ATM and currency exchange at the airport.
Entering by land, Afghanistan maintains open border crossings with all its neighbours except China. Most of Afghanistan's borders are so porous, you'll be generally looked on as more a novelty than a bureaucratic hindrance. Bear in mind that Afghanistan has 30 minutes' time difference with all its neighbours. Some borders are closed on certain days, and everything grinds to a halt at Friday lunch time.