You can use the Record object at render time to access the current DataSource record fields.
Record.collection|property|method
| Fields | Contains the list of field if the record | 
| SentenceCase | Sets or Gets how the receiver name should be formatted. | 
| Trim | Sets or Gets how record fields are trimmed. | 
| EmailAddress | Gets the displayable email address. | 
| Gets the email address. | |
| FullName | Gets the full name. | 
| FirstName | Gets the first name. | 
| LastName | Gets the last name. | 
| Fax | Gets the fax number. | 
| Mobile | Gets the mobile phone number. | 
The Record field is initialized by the DataSource object. Calculated Properties (EmailAddress, Email, FullName, etc.) will be automatically set before Mail_OnStartRender gets called.
<html>
Dear <%=Record.FirstName%><br>
I was wondering about what the weather's like in
<%=Record.Fields("City")%>?<br>
Regards,<br>
<%=Record.Fields("AccountManager")%>
</html>