Statistics Logging Scalability

My company is developing a centralized web platform to service our clients.  We currently use about 3Mb/s on our uplink at our ISP serving web pages for about 100 clients.  We'd like to offer them statistics that mean something to their businesses and have been contemplating writing our own statistics code to handle the task.

All statistics would be gathered at the page view level and we're implementing a HttpModule in ASP.Net 2.0 to handle the gather of the data.  That said, I'm curious to hear comments on writing this data (~500 bytes of log data/page request).  We need to write this data somewhere and then build a process to aggregate the data into a warehouse application used in our reporting system.  Google Analytics is out of the question because we do not want our hosting infrastructure dependant upon a remote server.  Web Trends et al. are too expensive for our clients.

I'm thinking of a couple of options.
1) Writing log data directly to a SQL Server 2000 db and having a Windows Service come in periodically to summarize and aggregate the data to the reporting server.  I'm not sure this will scale with higher load and that the aggregation process will timeout because of the number of inserts being sent to the table.
2) Write the log data to a structure in memory on the web server and periodically flush the data to the db.  The fear here is that the web server goes down and we lose all the data in memory.  Other fears are that the IIS processes and worker threads might mangle one another when contending for the memory system resource.
3) Don't use memory and write to a file instead.  Save the file handler as an application variable and use it for all accesses to the file.  Not sure about threading issues here as well and am reluctant to use anything which might corrupt a log file under load.
4) Add comment data to the IIS logs.  This theoretically should remove the threading issues but leaves me to think that the data would not be terribly useful once its in the IIS logs.

The major driver here is that we do not want to use any of the web sites and canned reports built into 90% of all statistics platforms.  Our users shouldn't have to "leave" the customer care portal we're creating just to see stats for their sites.  IFrames are not an option.   I'm looking for a solution that's not entirely complex, nor is it overly expensive and it will give me the access to the data we need to record on page views.  It has to scale with volume.  Thoughts are appreciated.