Both Peachtree and Quick Books use client/server or peer to peer and should work. I use an OLD version of peachtree and it operates flawlessly with my SME server.
Both Peachtree and Quickbooks recommend 5 or less users. It uses flat files and is pretty slow if more than 5 users are connected at the same time. How many concurent users will there be?
These programs are around $800 for a 5 user pack.
For around $3,500 Quick Books has an enterprise solution. It also uses flat files and peer to peer or client/server. It is recommended for up to 10 users.
Sourceforge has MANY Accounting and Point of sale programs written in perl, java, c, php, etc. Some are client/server but most are web based.
I did a quick search at sourceforge and found about a dozen that I will try out myself. My peachtree is 8 years old and really sucks for point of sale use. I have been thinking about upgrading but they now charge $700 for multi-user (multi-user was included 8 years ago at $159).
Tell me a bit more about the business (type of business, how many users, etc) and what the needs are (inventory, payroll, POS, etc). I will try to help you find the right software. Also, is it in the US or elsewhere?
Good Luck
Paul