Intel(R) Pentium(R) 4 CPU 2.80GHz best GPU
it is an old rig that cannot do much! but I want to get maximum out of it with hashcat instead of bulk of steel in the corner of my room so I am looking for the best match gpu which is compatible with it and hashcat or hashcat legacy on Lubuntu or ubuntu.

current specifications :

product: Intel(R) Pentium(R) 4 CPU 2.80GHz
          vendor: Intel Corp.

 System Memory [b]( I will upgrade this too)[/b]
          slot: System board or motherboard
          size: 512MiB
          capacity: 3GiB

description: VGA compatible controller
                product: 330 [Xabre] PCI/AGP VGA Display Adapter
                vendor: Silicon Integrated Systems [SiS]

current hashcat legacy benchmark (PART):

Initializing hashcat v2.00 with 1 threads and 32mb segment-size...

Device...........: Intel(R) Pentium(R) 4 CPU 2.80GHz
Instruction set..: x86_32
Number of threads: 1

Hash type: MD4
Speed/sec: 3.66M words

Hash type: MD5
Speed/sec: 3.19M words

Hash type: SHA1
Speed/sec: 2.74M words

Hash type: SHA256
Speed/sec: 1.77M words

Hash type: SHA512
Speed/sec: 664.14k words

Hash type: SHA-3(Keccak)
Speed/sec: 488.86k words

Hash type: GOST R 34.11-94
Speed/sec: 381.83k words

Hash type: SHA-1(Base64), nsldap, Netscape LDAP SHA
Speed/sec: 2.74M words

Hash type: SSHA-1(Base64), nsldaps, Netscape LDAP SSHA
Speed/sec: 2.50M words

Hash type: md5crypt, MD5(Unix), FreeBSD MD5, Cisco-IOS MD5
Speed/sec: 3.85k words

Hash type: sha256crypt, SHA256(Unix)
Speed/sec: 252 words

Hash type: sha512crypt, SHA512(Unix)
Speed/sec: 127 words

Hash type: bcrypt, Blowfish(OpenBSD)
Speed/sec: 511 words

That's a pretty efficient heating device you got there. But doing anything other than using that for heating is a waste of time (and power).
yes I use it for heating plus testing purposes.