Hardware needed for 15,000,000 record DB?

Hello,  :-)

Can someone help me spec out the hardware needed for a simple web-based
database app?

Basically, that application needs to lookup a single row by its primary key.
This would be fairly straightforward, except that the table needs to contain
up to 15 million records.  Each row will contain approximately 25  variable
length CHAR fields with perhaps a total of 3 to 4 kilobytes of data per row.

Updates will be done nightly via some sort of a batch process.

What kind of hardware would be needed for this sort of application? The
queries are not complex, it's just a lot of data.

Would a midrange Celeron processor with 256 MB RAM be sufficient? How would
backups work for a database this large?

Is PostgreSQL even the best database engine for this app? Perhaps MySQL? Or
maybe a Microsoft solution?

Thanks so much,
David