The easy and most common way to do this would be to changed the NTFS permissions on the folders, but since your users use universal credentials this will not work, do all users user the same credentials, or are there several accounts?
by “Universal Logins” I assume you mean everyone is using the same login? with everyone using the same login you will either take everyone’s rights away or you cannot take them away at all. what you will have to do is setup individual accounts for each user. then give modify rights to the creator and read only rights to everyone else. if your company does not have the money to get a windows server to do a true server-client network then it will be a large task setting up each user on each machine and keeping the passwords in sync with each machine. you could try using older hardware with the Mitel SME server. it is a simple way to get a very good network server up and running. I am currently using it on a 1GHz compaq server but that was a recent upgrade from an older 300MHz compaq server. it ran fine on the 300MHz server too. this system runs on a CentOS Linux operating system. the server comes with file and print services, LDAP directory, web server, ftp, email, antivirus, spam protection and ssh all built in. it works great and is free. there is a large user base and support if needed, (though support must be purchased if you need to contact them directly, but the documentation and user forums are a great deal of help). If you have a tape backup setup it will do automatic backups to tape too. but you can also do a manual backup to your desktop if needed. you can read up on the system at contribs.org. then go to their About section to get a background on it.
hope that helps, Buddy