Lead Liaison is compatible with many editions of Salesforce.com including Group, Professional, Enterprise, and Unlimited. View available Salesforce.com editions here: http://www.salesforce.com/crm/editions-pricing.jsp
Lead Liaison requires one Salesforce.com user account to be used as the sync account. The sync account is the account used to send data bidirectional, from Salesforce.com to Lead Liaison and from Lead Liaison to Salesforce.com. Salesforce.com requires credentials to be updated every 90 days. If credentials for the sync account expire they must be updated otherwise syncing will fail.