There are several different ways. The simplest one is probably something like:

--Convert Int to Hex:

SELECT CONVERT(VARCHAR(8),CONVERT(VARBINARY(4), 345678),2)

--Convert Hex to Int:

SELECT CONVERT(INT,CONVERT(VARBINARY(4),'0005464E',2))

You can find others, likely some better approaches - try searching on: SQL Server Hex to Decimal

Sue