Huge Performance Issue

I have a medical DB with the loads 150,000 transactions per month. Each month, I load the tranactions into a table for the current year. I also have to update records for prior months based on current month information.

For example, out of 186,000 dump records...150,000 will be loaded into the main table and 36,000 will be used to update records already loaded into the main table.

The tables have 90 columns, I have a clustered PK using [Soc_Sec_Number] & [Month] & [Row Index]. I need the row index counter (like auto number in MS Access) because I can have multiple transactions per month for the same Soc Sec Number.

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My steps are

1) Load 150,000 records into main table (For december, this makes the table have 1,800,000 rows
2) Run queries for the remaining 36,000 rows to update records already loaded into the table containing the 1,800,000 rows.
3) The 36,000 queries have to be splits depending upon the update type code, So I am actually running 6 queries using 6,000 rows each against the 1,800,000 records.

The update queries are using inner joins with [Soc Sec #] and [Date], part of my composite Primary Key on both tables.

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Problem

This process takes forever, about 4 hours per monthly update. As the months go out, the main table gets larger and the time increases. It took almost 24 hrs to get from January 2004 to June 2004.

I am running Sql Server on my PC, no seperate workstation. My PC has 2.8 GHZ with about 1 Gig in RAM. Could my PC specs be too low. I noticed that the task mamager shows sqlservr.exe using over 657,000 mb of RAM when running.

I also ran a simple Select MAX(Soc_Sec_Number) query that took over 5 minutes. This is way too long especially since Soc_sec_Number is part of the composite PK.

Could my queries actually take that long or are my pC specs too low. MY PC seemed to freeze after the JUNE update? Any help appreciated.