9x uses SMB1 so you'd have to enable that on your Windows 7 machine which is a security risk. SMB1 uses the same services and ports as SMB2+ but I suppose if you lock down ports 137,138 and 139 (since those should be the ones 9x uses to access shares) to specific IPs you'd probably be fine.
Additionally you'll need to decrease NTLM security in gpedit and also create a user account on the Windows 7 machine for the 9x machine
If you don't want to use SMB you can use FTP or SFTP.
If using FreeNAS then I use the below:
SYSTEM->TUNABLES (MIGHT NOT BE NECESSARY)
Variable: freenas.services.smb.config.server_min_protocol
Value: NT1
Type: sysctl
COmment: SMB1
SERVICES->SMB
Auxilary Parameters->
min protocol = NT1
lanman auth = Yes
client lanman auth = Yes
client plaintext auth = Yes
The above options (one may only be necessary) will allow access to Freenas from 9x clients. The below smbpasswd command will allow access to shares requiring authentication. If the below smbpasswd does not work then your only option is to setup another share and allow guest access:
Create guest share and allow guest access. Change permissions for "Everyone" to write access
From FreeNAS command prompt:
smbpasswd -a username
Use the same username on guest as on the FreeNAS host