In the preferred computer system, the user is provided with a separate Internet-accessible entity referred to here as the "personal page." A personal page, preferably, includes memory for storing information related to the user. For example, on his/her personal page the user indicates what he/she wishes to purchase, possibly along with other criteria associated with the purchase, such as, for example, a time that the purchase should take The user is provided with the ability to create personalized bidding rules that vendors that offer goods and services must respect. Vendors have the ability to specify similar criteria, which describe the goods and/or services they offer. Vendors can indicate, for example, the prices of their goods, times and places that their services are available, etc. Preferably, these specifications, called "vendor scripts," are embodied in active software/data entities (agents) that traverse sites on the Internet visiting sites hosting users' personal pages. Thus, preferably, vendor software/data agents (comprising vendor scripts) are the mobile, active elements in the system and purchasing requirements are stationary and more passive in comparison.