You may want to buy or top up a SIM card at Entel because getting online is pricey (B$6 per hour) and often frustratingly slow. If you need a computer, Internet Cyber Ronaldo is your best bet.
The most convenient of the two ATMs in town is a block north of the plaza at Banco Unión. You can get cash advances at Prodem, but only on Visa and MasterCard (including Visa debit cards). It also does Western Union transfers and changes cash.
Workers at the tourist office are happy to answer questions and keen to advise on responsible tourism, but they're short on material. For information on Parque Nacional Madidi, head to the Sernap office in San Buenaventura.