Table viewer for big sorted tables

Hi all!

I want to write a PostgreSQL based program in C++ on Linux system,
but I have a problem:

For example, user must fill up the form.
One of the fields is product_symbol that is a key in another table (indexed).

I want user to select the correct product_symbol from list, that
show product_symbol and corresponding fields from products table
in sorted way.
In other words, I want to write table viewer thet allow user to walk on
entire table using cursor keys, Pgup, PgDown and Home/End.

I first thought, that scrollable cursor would be good. I was wrong,
because first fetch from cursor took long time if table
had big number of rows. Cursors are also insensitive :(
and re-opening would take long time again...

I'm thinking about sequentially reads from table with
select statement with where clause.
BUT I don't know how to fast obtain the next (in order) value of product_symbol
(next to current value)

The slow version is:
SELECT min(product_symbol) FROM products WHERE product_name > 'current_product';

This take about 1 second in table with 100 000 records (2 columns only).
If I want to show 20 rows at the same time on screen - this take 20 seconds :(

Any suggestions ???

TIA

--
Ryszard Kurek
rychu(at)sky(dot)pl