MS T-SQL how to convert an nvarchar to hex and then to integer?

I am using MS SQL-7
I am getting the error: Syntax error converting the nvarchar value '41801d37' to a column of data type int.
My question in summary is: How to convert a data of type "nvarchar" that represent a hex value to an integer vlaue?
In other words how to convert 41801d37 to 1098915127

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Now I am going to provide some details:
I have a table with a column called "hexcode"
The data type in this column is varbinary with a length of 12, and looks like this:
0x1A000000FCFF12000200371D8041591B403C381D8041591B403C
I needed to get rid of the leading 23 characters, and I did it like this:
SELECT SUBSTRING(master.dbo.fn_varbintohexstr(hexcode),23,32)
That gives me the following:371D8041591B403C381D8041591B403C

I use more string operations as follows:

select  HexCode,
          Convert(int,(Lo1+Lo2+Lo3+Lo4)) as NewIntCode
from
(
SELECT ObjectIdHi, objectIdLo, uiName, HexCode,
Substring(substring(master.dbo.fn_varbintohexstr(HexCode),23,8), 7, 2) Lo1,
Substring(substring(master.dbo.fn_varbintohexstr(HexCode),23,8), 5, 2) Lo2,
Substring(substring(master.dbo.fn_varbintohexstr(HexCode),23,8), 3, 2) Lo3,
Substring(substring(master.dbo.fn_varbintohexstr(HexCode),23,8), 1, 2) Lo4
FROM MyTable
)
as NewTable

My problem is that when I run the query I get the error:
Syntax error converting the nvarchar value '41801d37' to a column of data type int.