SQL problem: Converting timestamp field into double value

[Dr.Rock]

I'm writing a VB app which sends an SQL statement to MS SQL Server:

strSQL = "select * from systemevents where timestamp >= " + CStr(LastEventTimestampRead) + " ORDER BY timestamp"

strSQL = the SQL statement
timestamp = field with date and time value, in date and time format.
LastEventTimestampRead = double variable from external source, representing a time value.

How do I convert the timestamp field value into a DOUBLE type value within the SQL statement, so I can compare it with the LastEventTimestampRead variable? I tried CDbl but that's an Access command that's not compatible with SQL Server.

Thanks.