America Online Inc has once again leveraged its burgeoning user base to persuade a company to pay it a guaranteed sum for an exclusive spot in its online service and its web site. This time, Software.net, an online and traditional reseller of business and consumer software, will pay AOL $21m in guaranteed payments, plus a share of advertising revenues for exclusive and non-exclusive space on AOL’s services. The areas include computing, tax preparation, software downloads, personal finance, games and file search on the web site. In return, AOL will invest up to $2m in privately-held Software.net through its newly-created AOL Investments unit. San Jose, California-based Software.net says it will offer both down- loads and traditional packaged software. AOL’s shares closed down $1.875 at $61.625 yesterday, mainly because Merrill Lynch downgraded the stock from accumulate to neutral.